bnxt_en: Fix aggregation buffer leak under OOM condition.

For every RX packet, the driver replenishes all buffers used for that
packet and puts them back into the RX ring and RX aggregation ring.
In one code path where the RX packet has one RX buffer and one or more
aggregation buffers, we missed recycling the aggregation buffer(s) if
we are unable to allocate a new SKB buffer.  This leads to the
aggregation ring slowly running out of buffers over time.  Fix it
by properly recycling the aggregation buffers.

Fixes: c0c050c5 ("bnxt_en: New Broadcom ethernet driver.")
Reported-by: Rakesh Hemnani <rhemnani@fb.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>