Do not return unlocked/unreferenced lle in arpresolve/nd6_storelladdr -
  return lle flags IFF needed.
Do not pass rte to arpresolve - pass is_gateway flag instead.
Fix build broken by r275195.
Correctly define constants.

MFC after:	1 week
Merge remote-tracking branch 'freebsd/master' into hardened/current/master