bnxt_en: Add bnxt_l2_filter hash table.

The current driver only has an array of 4 additional L2 unicast
addresses to support the netdev uc address list.  Generalize and
expand this infrastructure with an L2 address hash table so we can
support an expanded list of unicast addresses (for bridges,
macvlans, OVS, etc).  The L2 hash table infrastructure will also
allow more generalized n-tuple filter support.

This patch creates the bnxt_l2_filter structure and the hash table.
This L2 filter structure has the same bnxt_filter_base structure
as used in the bnxt_ntuple_filter structure.

All currently supported L2 filters will now have an entry in this
new table.

Note that L2 filters may be created for the VF.  VF filters should
not be freed when the PF goes down.  Add some logic in
bnxt_free_l2_filters() to allow keeping the VF filters or to free
everything during rmmod.

Reviewed-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>