net/mlx5e: Fix endianness when calculating pedit mask first bit

The field mask value is provided in network byte order and has to
be converted to host byte order before calculating pedit mask
first bit.

Fixes: 88f30bbc

 ("net/mlx5e: Bit sized fields rewrite support")
Signed-off-by: Maor Dickman <maord@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>