netinet6: call lle_event eventhandler after updating state

Fix nd6_na_input() eventhandler call: run eventhandler after lle
state transition.

Old behaviour (as seen by event handler):

• fe80::5054:ff:fe8c:63e9 dev vtnet0 lladdr 52:54:00:8c:63:e9 INCOMPLETE

New behaviour:

• fe80::5054:ff:fe8c:63e9 dev vtnet0 lladdr 52:54:00:8c:63:e9 REACHABLE

MFC after: 2 weeks

(cherry picked from commit db98b4205093a6ee201ce0b8d83c77d5b730d7cb)