Make most of functions const correct (#714)

* Make most of the functions const correct

Used clang-tidy and sonarlint to help find places where const could
pretty easily applied. Also lot of hand work.

This commit does not yet touch handlers and typedefs of those.

* Fix Arduino uno handler_who_is() has extra parenthesis

For some reason there is extra parenthesis. Remove it this is more
likely buildable.

* Bugfix/bacapp: Fix uninitilized array_index

We have changed bacapp_snprintf_value() to be const correct. After that
we got

```
/home/runner/work/bacnet-stack/bacnet-stack/src/bacnet/bacapp.c:3183:27: warning: 4th function call argument is an uninitialized value [core.CallAndMessage]
                ret_val = bacapp_snprintf_weeklyschedule(
                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning generated.
```

So analyzer could now spot that we do not actually initilize array_index
at all. Fix this by setting array_index to zero. Note that I actually do
not know if zeroing is right thing to do here. I choose zero as if this
has worked before it is most likely that it will work with zero value.

* cmake: Add and ignore Wwrite-strings compiler option

Wwrite-strings helps find places where const correctness is broken.

Example it will warn about these

```C

void func1(char* str);

func("test") /* "test" is const so we should not pass it to func1().

char* func2()
{
  return "test"; /* func2() should return const char*.
}
```

We still need to ignore it as not all are fixed but let's add it already
so we remember that it should be opened at some point.

---------

Co-authored-by: Kari Argillander <kari.argillander@fidelix.com>

apps/router-ipv6/main.c

@@ -156,7 +156,7 @@ static bool port_find(uint16_t snet, BACNET_ADDRESS *addr)
  * @param snet - router port SNET
  * @param addr - address of port at the net to be added
  */
-static void port_add(uint16_t snet, BACNET_ADDRESS *addr)
+static void port_add(uint16_t snet, const BACNET_ADDRESS *addr)
 {
     DNET *port = NULL;
     DNET *dnet = NULL;
@@ -204,7 +204,7 @@ static void port_add(uint16_t snet, BACNET_ADDRESS *addr)
  * @param net - net to be added
  * @param addr - address of router at the net to be added
  */
-static void dnet_add(uint16_t snet, uint16_t net, BACNET_ADDRESS *addr)
+static void dnet_add(uint16_t snet, uint16_t net, const BACNET_ADDRESS *addr)
 {
     DNET *dnet = NULL;
     DNET *port = NULL;
@@ -398,7 +398,8 @@ static void send_i_am_router_to_network(uint16_t snet, uint16_t net)
  *  Optionally may designate a particular router destination,
  *  especially when ACKing receipt of this message type.
  */
-static void send_initialize_routing_table_ack(uint8_t snet, BACNET_ADDRESS *dst)
+static void send_initialize_routing_table_ack(
+    uint8_t snet, const BACNET_ADDRESS *dst)
 {
     BACNET_ADDRESS dest;
     bool data_expecting_reply = false;
@@ -458,7 +459,10 @@ static void send_initialize_routing_table_ack(uint8_t snet, BACNET_ADDRESS *dst)
  * @param reject_reason [in] One of the BACNET_NETWORK_REJECT_REASONS codes.
  */
 static void send_reject_message_to_network(
-    uint16_t snet, BACNET_ADDRESS *dst, uint8_t reject_reason, uint16_t dnet)
+    uint16_t snet,
+    const BACNET_ADDRESS *dst,
+    uint8_t reject_reason,
+    uint16_t dnet)
 {
     BACNET_ADDRESS dest;
     bool data_expecting_reply = false;
@@ -571,9 +575,9 @@ static void send_who_is_router_to_network(uint16_t snet, uint16_t dnet)
  * @param npdu_len [in] The length of the remaining NPDU message in npdu[].
  */
 static void who_is_router_to_network_handler(uint16_t snet,
-    BACNET_ADDRESS *src,
-    BACNET_NPDU_DATA *npdu_data,
-    uint8_t *npdu,
+    const BACNET_ADDRESS *src,
+    const BACNET_NPDU_DATA *npdu_data,
+    const uint8_t *npdu,
     uint16_t npdu_len)
 {
     DNET *port = NULL;
@@ -752,7 +756,7 @@ static void network_control_handler(uint16_t snet,
  * @param src [in] The BACNET_ADDRESS of the message's original src.
  */
 static void routed_src_address(
-    BACNET_ADDRESS *router_src, uint16_t snet, BACNET_ADDRESS *src)
+    BACNET_ADDRESS *router_src, uint16_t snet, const BACNET_ADDRESS *src)
 {
     unsigned int i = 0;