net/mlx4_core: Don't allow to VF change global pause settings

Currently changing global pause settings is done via SET_PORT
command with input modifier GENERAL. This command is allowed
for each VF since MTU setting is done via the same command.

Change the above to the following scheme: before passing the
request to the FW, the PF will check whether it was issued
by a slave. If yes, don't change global pause and warn,
otherwise change to the requested value and store for
further reference.

Signed-off-by: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>