bnxt_en: Use event bit map in RX path.

In the current code, we have separate rx_event and agg_event parameters
to keep track of rx and aggregation events.  Combine these events into
an u8 event mask with different bits defined for different events.  This
way, it is easier to expand the logic to include XDP tx events.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>