NFC: Do not take the genl mutex from the netlink release notifier

The netlink notifier is atomic so we must not sleep in that context.
Also we know that Any netlink packets arriving to us will be purged when
the notifier is called, so we don't need to take the mutex.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>