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>

ports/linux/bip6.c

@@ -188,7 +188,7 @@ void bip6_get_my_address(BACNET_ADDRESS *addr)
  *
  * @param addr - network IPv6 address
  */
-bool bip6_set_addr(BACNET_IP6_ADDRESS *addr)
+bool bip6_set_addr(const BACNET_IP6_ADDRESS *addr)
 {
     return bvlc6_address_copy(&BIP6_Addr, addr);
 }
@@ -208,7 +208,7 @@ bool bip6_get_addr(BACNET_IP6_ADDRESS *addr)
  *
  * @param addr - network IPv6 address
  */
-bool bip6_set_broadcast_addr(BACNET_IP6_ADDRESS *addr)
+bool bip6_set_broadcast_addr(const BACNET_IP6_ADDRESS *addr)
 {
     return bvlc6_address_copy(&BIP6_Broadcast_Addr, addr);
 }
@@ -234,7 +234,8 @@ bool bip6_get_broadcast_addr(BACNET_IP6_ADDRESS *addr)
  * @return Upon successful completion, returns the number of bytes sent.
  *  Otherwise, -1 shall be returned and errno set to indicate the error.
  */
-int bip6_send_mpdu(BACNET_IP6_ADDRESS *dest, uint8_t *mtu, uint16_t mtu_len)
+int bip6_send_mpdu(
+    const BACNET_IP6_ADDRESS *dest, const uint8_t *mtu, uint16_t mtu_len)
 {
     struct sockaddr_in6 bvlc_dest = { 0 };
     uint16_t addr16[8];
@@ -259,7 +260,7 @@ int bip6_send_mpdu(BACNET_IP6_ADDRESS *dest, uint8_t *mtu, uint16_t mtu_len)
     bvlc_dest.sin6_scope_id = BIP6_Socket_Scope_Id;
     debug_print_ipv6("Sending MPDU->", &bvlc_dest.sin6_addr);
     /* Send the packet */
-    return sendto(BIP6_Socket, (char *)mtu, mtu_len, 0,
+    return sendto(BIP6_Socket, (const char *)mtu, mtu_len, 0,
         (struct sockaddr *)&bvlc_dest, sizeof(bvlc_dest));
 }