bnxt_en: Add support for L2 rewrite

This patch adds support for packet edit offload of L2 fields (src mac &
dst mac, also referred as L2 rewrite). Only when the mask is fully exact
match for a field, the command is sent down to the adapter to offload
such a flow. Otherwise, an error is returned.

v2: Fix pointer alignment issue in bnxt_fill_l2_rewrite_fields() [MChan]

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