ionic: stop devlink warn on mgmt device

If we don't set a port type, the devlink code will eventually
print a WARN in the kernel log.  Because the mgmt device is
not really a useful port, don't register it as a devlink port.

Fixes: b3f064e9 ("ionic: add support for device id 0x1004")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>