net/mlx5: Eswitch, avoid redundant mask

misc_params.source_port is a 16 bit field already so no need for
redundant masking against 0xffff. Also change local variables type to
u16.

Signed-off-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>