Remove -Wno-unused-parameter

Introduced UNUSED macro with cast to void in commoh.h for internal
use. Used cast to void directly in those files which do not
include common.h. Although this change doesn't fix semantic issues
with unused function parameters, it does explicitly mark all those
places, which might require attention in future.

src/tls_openssl.c

@@ -203,6 +203,8 @@ void tls_free(tls_t *tls)
 
 int tls_set_credentials(tls_t *tls, const char *cafilename)
 {
+    UNUSED(tls);
+    UNUSED(cafilename);
     return -1;
 }
 
@@ -305,6 +307,7 @@ int tls_write(tls_t *tls, const void *const buff, const size_t len)
 
 int tls_clear_pending_write(tls_t *tls)
 {
+    UNUSED(tls);
     return 0;
 }