nfp: only report pause frame configuration for physical device

Only report pause frame configuration for physical device. Logical
port of both PCI PF and PCI VF do not support it.

Fixes: 9fdc5d85

 ("nfp: update ethtool reporting of pauseframe control")
Signed-off-by: Yu Xiao <yu.xiao@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>