rtpdec: Remove a woefully misplaced comment

The code below the comment does not at all relate to statistics,
and even if moved to the right place, the comment adds little
value.

Signed-off-by: Martin Storsjö <martin@martin.st>
rtpdec: Simplify insertion into the linked list queue

By using a pointer-to-pointer, we avoid having to keep track
of the previous packet separately.

Signed-off-by: Martin Storsjö <martin@martin.st>
rtpdec: Handle more received packets than expected when sending RR

Without this, we'd signal a huge loss rate (due to unsigned
wraparound) if we had received one packet more than expected (that
is, one seq number sent twice). The code has a check for lost_interval
<= 0, but that doesn't do what was intended as long as the variable is
unsigned.

Signed-off-by: Martin Storsjö <martin@martin.st>