T.140: Fix format ref and memory leaks.

* channel.c:ast_sendtext(): Fix T.140 SendText memory leak.

* format_compatibility.c: T.140 RED and T.140 were swapped.

* res_rtp_asterisk.c:rtp_red_init(): Fix ast_format_t140_red ref leak.

* res_rtp_asterisk.c:rtp_red_init(): Fix data race after starting periodic
scheduled red_write().

* res_rtp_asterisk.c: Some other minor misc tweaks.

Change-Id: Ifa27a2e0f8a966b1cf628607c86fc4374b0b88cb