net: ipa: kill replenish_saved

The replenish_saved field keeps track of the number of times a new
buffer is added to the backlog when replenishing is disabled.  We
don't really use it though, so there's no need for us to track it
separately.  Whether replenishing is enabled or not, we can simply
increment the backlog.

Get rid of replenish_saved, and initialize and increment the backlog
where it would have otherwise been used.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>