Use llt_prepare_static_entry method to prepare valid per-af static entry.
Simplify lle lookup/create api by using addresses instead of sockaddrs.
* Do not assume lle has sockaddr key after struct lle:
   use llt_fill_sa_entry() llt method to store lle address in sa.
* Eliminate L3_ADDR macro and either reference IPv4/IPv6 address
   directly from lle or use newly-created llt_fill_sa_entry().
* Do not store sockaddr inside arp/ndp lle anymore.