res_pjsip_sdp_rtp: Improve detecting of lack of RTP activity

Change RTP timer behavior for detecting RTP only after two-way
SDP channel establishment. Ignore detecting after receiving 183
with SDP or while direct media is used.
Make rtp_timeout and rtp_timeout_hold options consistent to rtptimeout
and rtpholdtimeout options in chan_sip.

ASTERISK-26689 #close
ASTERISK-29929 #close

Change-Id: I07326d5b9c40f25db717fd6075f6f3a8d77279eb