net/mlx5_core: Use port number in the query port mtu helpers

Extend the function prototypes for max and operational mtu to take the
local port number. In the Ethernet driver is this hard coded to one,
since ConnectX4 Ethernet devices are always function-per-port.
The IB driver also serves older devices (ConnectIB) which isn't such,
and hence the part can vary.

Signed-off-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>