* Fix off nominial ref leak of new_type in
ast_rtp_codecs_payloads_set_m_type().

* No need to lock static_RTP_PT_lock in
ast_rtp_codecs_payloads_set_m_type() and
ast_rtp_codecs_payloads_set_rtpmap_type_rate() before the payload type
parameter sanity check.

* No need to create ast_rtp_payload_type ao2 objects with a lock since the
lock is not used.

Change-Id: I64dd1bb4dfabdc7e981e3f61448beac9bb7504d4