Lock if_addrhead when iterating, and where necessary acquire and release ifadr references in if_sppp.
Lock if_addrhead when iterating, and where necessary acquire and release
ifadr references in if_sppp.

MFC after:	6 weeks

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase