Fix misspelled function

switch_rtp_set_invalid_handler has been misspelled as
switch_rtp_set_invald_handler going all the way back to the
beginning.  So while it's possible that someone somewhere could be
relying on this misspelling, I think it's more likely that no one has
used it much and that's why it wasn't spotted.  We don't even use it
ourselves anywhere anymore.

Introduced in commit: 828e03715f

src/switch_rtp.c

@@ -4096,7 +4096,7 @@ SWITCH_DECLARE(uint32_t) switch_rtp_get_default_payload(switch_rtp_t *rtp_sessio
 	return rtp_session->payload;
 }
 
-SWITCH_DECLARE(void) switch_rtp_set_invald_handler(switch_rtp_t *rtp_session, switch_rtp_invalid_handler_t on_invalid)
+SWITCH_DECLARE(void) switch_rtp_set_invalid_handler(switch_rtp_t *rtp_session, switch_rtp_invalid_handler_t on_invalid)
 {
 	rtp_session->invalid_handler = on_invalid;
 }