v4l2bufferpool: Also update num_buffers for import cases

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2bufferpool: Don't deactivate otherpool

We should not stop the otherpool unless we also stop our own
pool, otherwise it will never get restarted.

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2allocator: Fix use of atomic active marker

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2transform: Flush buffer pools on flush stop

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2: Split flush in start/stop_streaming

This allow calling start streaming later for capture device. Currently it breaks
in dmabuf-import because downstream is holding a buffer that will only be
released after stream-start.

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2transform: Don't leak pool if activation failed

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2videodec: Don't lock the decoder when stopping task

That src pad task may need to take the lock when being pulled
down. takeing that lock can lead to a deadlock.

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2videodec: Print the flow return causing the loop to leave

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2videodec: Handle start_streaming error

https://bugzilla.gnome.org/show_bug.cgi?id=730207
v4l2bufferpool: Update pool limit with hardware requiremenst

If the driver need more buffers than requested by the config,
update the pool min/max values. The minimum value for the pool
could be provided either by the driver or by the pool. This is
best effort for drivers that don't support
CID V4L2_CID_MIN_BUFFERS_FOR_CAPTURE.

https://bugzilla.gnome.org/show_bug.cgi?id=730200
v4l2: Cleanup M2M properties

M2M devices were sharing the same properties as src and sink. Most of
these made no sense. This patch reduces the number of propeties and
makes io-mode clearer by having capture-io-mode and output-io-mode. This
also accidently fixed a bug in gstv4l2transform io-mode code, where the
capture io-mode could not be set.

https://bugzilla.gnome.org/show_bug.cgi?id=729591
rtpsession: update last_activity when sending RTP

Also update last_activity when doing something with the internal
source to make sure don't timeout early.

See https://bugzilla.gnome.org/show_bug.cgi?id=730217
rtspsrc: always use a random ssrc for the internal session

Use a random SSRC different than 0 for the internal session SSRC.

https://bugzilla.gnome.org/show_bug.cgi?id=730212
v4l2allocator: Don't trace twice the same message
v4l2videodec: Handle flush while in start_streaming

We need to handle the case where a flush occure while the streaming
thread is being brought up. In this case, the flushing state of the poll
object is cleared. To solve this, we simply set the capture poll to flushing
again, this way we know the thread will exit. The decoder streamlock
is used to synchronize with handle frame.