Scope related cleanup in nd6_is_new_addr_neighbor():

• since we assume that addresses doesn't contains embedded zone ids, link-local addresses are always neighbors. So, remove sa6_recoverscope() and in6_setscope() calls;
• use in6_localip() to check that address matches one of our addresses;
• use in6ifa_ifpwithdstaddr() instead of ifa_ifwithdstaddr().