net: Pass ndm_state to route netlink FDB notifications.

Before this change applications monitoring FDB notifications
were not able to determine whether a new FDB entry is permament
or not:
bridge fdb add f1:f2:f3:f4:f5:f8 dev sw0p1 temp self
bridge fdb add f1:f2:f3:f4:f5:f9 dev sw0p1 self

bridge monitor fdb

f1:f2:f3:f4:f5:f8 dev sw0p1 self permanent
f1:f2:f3:f4:f5:f9 dev sw0p1 self permanent

With this change ndm_state from the original netlink message
is passed to the new netlink message sent as notification.

bridge fdb add f1:f2:f3:f4:f5:f6 dev sw0p1 self
bridge fdb add f1:f2:f3:f4:f5:f7 dev sw0p1 temp self

bridge monitor fdb
f1:f2:f3:f4:f5:f6 dev sw0p1 self permanent
f1:f2:f3:f4:f5:f7 dev sw0p1 self static

Signed-off-by: Hubert Sokolowski <hubert.sokolowski@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>