net/mlx5: Don't write read-only fields in MODIFY_HCA_VPORT_CONTEXT command

The MODIFY_HCA_VPORT_CONTEXT uses field_selector to mask fields needed
to be written, other fields are required to be zero according to the
HW specification. The supported fields are controlled by bitfield
and limited to vport state, node and port GUIDs.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>