On the first session server, the first payload packet gets queued
but the Rx callback will only be invoked when the second packet
is received.
By initializing enqueue_epoch in the session, we can make sure that
the RX callback will be invoked for the first packet as well.
Change-Id: I60e2cf8d4d2ca71d461ca003d459c8e6e6956a4d
Signed-off-by: Andreas Schultz <aschultz@warp10.net>