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/main.c

@@ -43,7 +43,7 @@ int port_count;
 
 void print_help(void);
 
-bool read_config(char *filepath);
+bool read_config(const char *filepath);
 
 bool parse_cmd(int argc, char *argv[]);
 
@@ -53,7 +53,7 @@ bool init_router(void);
 
 void cleanup(void);
 
-void print_msg(BACMSG *msg);
+void print_msg(const BACMSG *msg);
 
 uint16_t process_msg(BACMSG *msg, MSG_DATA *data, uint8_t **buff);
 
@@ -61,7 +61,7 @@ uint16_t get_next_free_dnet(void);
 
 int kbhit(void);
 
-inline bool is_network_msg(BACMSG *msg);
+inline bool is_network_msg(const BACMSG *msg);
 
 int main(int argc, char *argv[])
 {
@@ -201,7 +201,7 @@ void print_help(void)
         "-s, --stopbits <1|2>\n\tspecify MSTP port stopbits\n");
 }
 
-bool read_config(char *filepath)
+bool read_config(const char *filepath)
 {
     config_t cfg;
     config_setting_t *setting;
@@ -725,11 +725,11 @@ void cleanup(void)
     pthread_mutex_destroy(&msg_lock);
 }
 
-void print_msg(BACMSG *msg)
+void print_msg(const BACMSG *msg)
 {
     if (msg->type == DATA) {
         int i;
-        MSG_DATA *data = (MSG_DATA *)msg->data;
+        const MSG_DATA *data = (const MSG_DATA *)msg->data;
 
         if (data->pdu_len) {
             PRINT(DEBUG, "Message PDU: ");
@@ -821,10 +821,10 @@ int kbhit(void)
     return bytesWaiting;
 }
 
-bool is_network_msg(BACMSG *msg)
+bool is_network_msg(const BACMSG *msg)
 {
     uint8_t control_byte; /* NPDU control byte */
-    MSG_DATA *data = (MSG_DATA *)msg->data;
+    const MSG_DATA *data = (const MSG_DATA *)msg->data;
 
     control_byte = data->pdu[1];