mlx4_core: Disable SENSE_PORT for multifunction devices

In the current driver, the SENSE_PORT firmware command is issued as a
"wrapped" command, but the command handling code doesn't have a
wrapper, so it will never do anything other than log an error message.
The latest ConnectX-3 2.11.500 firmware reports the SENSE_PORT
capability even in multi-function (SR-IOV) mode, so the driver will
try to issue the command.

At least until the driver has a proper wrapper for SENSE_PORT, make
sure we disable the command for multi-function devices.

Signed-off-by: Roland Dreier <roland@purestorage.com>