net/mlx5e: Bit sized fields rewrite support

This patch doesn't change any functionality, but is a pre-step for
adding support for rewriting of bit-sized fields, like DSCP and ECN
in IPv4 header, similar fields in IPv6, etc.

Signed-off-by: Dmytro Linkin <dmitrolin@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>