return error in server_start if pthread_create failed

Also, no need to change the state before thread creation, since the
server thread doesn't care about the state attribute.
destroy sccp_tech.capabilities if channel tech fails to register
no need to allocate a lock for session ao2 object
don't try to answer an already answered subchan
move transmit_speaker_mode into do_answer

The speaker is now only turned on if do_answer is succesful.
add do_newcall_options

Similar to do_answer/do_answer_options.
only write frame for active subchan
remove state member of struct sccp_line
don't queue DTMF in ringout state if progress was not indicated
move resuming member into flags
move autoanswer member into flags
move transferring member into flags
simplify sccp_session_read_sock
add destroyed state to device

I believe it makes more sense for it to be a state of its own instead of
a flag.
only answer subchan if in state RINGIN
Merge branch '5203-rtp-instance-leak'