net: mlx4: Staticize local functions

These local functions are used only in this file.
Fix the following sparse warnings:

drivers/net/ethernet/mellanox/mlx4/cmd.c:803:5: warning: symbol 'MLX4_CMD_UPDATE_QP_wrapper' was not declared. Should it be static?
drivers/net/ethernet/mellanox/mlx4/cmd.c:812:5: warning: symbol 'MLX4_CMD_GET_OP_REQ_wrapper' was not declared. Should it be static?
drivers/net/ethernet/mellanox/mlx4/cmd.c:1547:5: warning: symbol 'mlx4_master_immediate_activate_vlan_qos' was not declared. Should
it be static?

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-By: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>