ac3parse: correctly handle timestamps when parsing x-private1-ac3

... the way it has always worked fine in a52dec.
check: add rtpsession test

Add a basic rtpsession test to ensure that RR blocks are generated when
multiple SSRC senders are active.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=711270
gstrtpsession: send custom upstream event "GstRTPCollision" on send_rtp_sink pad

See https://bugzilla.gnome.org/show_bug.cgi?id=711560
rtpsession: remove collision reconfigure event

Remove bogus reconfigure event on collision, we don't want to send the event on
the receiving RTP pad and the collision event is now handling this
case.

See https://bugzilla.gnome.org/show_bug.cgi?id=711560
v4l2: init v4l2_buffer to 0x0 before ioctl

https://bugzilla.gnome.org/show_bug.cgi?id=712137
rtspsrc: Use the synced buffer mode in auto mode if a clock provider is in the SDP
gstpay: only send one caps

Only send one caps in a packet. Two caps can happen when setcaps is called and
the config-interval expires at the same time.
jitterbuffer: advance expected seqnum after dropping

After dropping a buffer, move our expected seqnum

Conflicts:
	gst/rtpmanager/gstrtpjitterbuffer.c
v4l2object: print FOURCC_FORMAT when enumerating

https://bugzilla.gnome.org/show_bug.cgi?id=712206
rtpjitterbuffer: implement rtx statistics
rtpjitterbuffer: rename property to 'stats'

This makes the unit test work.
We can later also add more stats, not specific to retransmission.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=711411