endpoint->hello information memory leak when coap_free_endpoint() called

Information set up in the pseudo session held in endpoint->hello is not freed
off when coap_free_endpoint() is called.

A solution is to split coap_session_free() into two parts with
coap_session_free() calling a new function coap_session_mfree().

Then coap_mfree_endpoint() can call coap_session_mfree() to free off the
endpoint specific hello information.

Makefile.am

Add coap_mfree_endpoint and coap_session_mfree to the CTAGS_IGNORE list.

libcoap-2.{map|sym}

Remove coap_mfree_endpoint as it is not a public function

include/coap2/coap_session.h

Add in new coap_session_mfree() function definition

src/coap_io.c

Call coap_session_mfree() from within coap_mfree_endpoint()

src/coap_session.c

Move some of the functionality out of coap_session_free() into a new
function coap_session_mfree() and  call coap_session_mfree().

include/coap2/coap_session.h

@@ -368,6 +368,7 @@ coap_session_t *coap_session_get_by_peer(struct coap_context_t *ctx,
   const struct coap_address_t *remote_addr, int ifindex);
 
 void coap_session_free(coap_session_t *session);
+void coap_session_mfree(coap_session_t *session);
 
  /**
   * @defgroup cc Rate Control