enic: fix link state change

enic: fix link state change

When the enic was disabled, link notification was correctly disabled
in the NIC but the software indicator that it was disabled was not
updated (vdev->notify_pa not set to 0). When the link came back up,
enic did not re-enable notification in the NIC.

This affected bonding when a enic slave device link bounced.

The fix is to unconditionally enable notification when the enic is
enabled.

Fixes: 9913fbb91df0 ("enic/base: common code")
Signed-off-by: John Daley <johndale@cisco.com>
Reviewed-by: Nelson Escobar <neescoba@cisco.com>