MFC r325614:
Multiple fixes for using IPv6 link-local addresses with RDMA.

1. Fail to resolve RDMA address if rtalloc1() returns the loopback

device, lo0, as the gateway interface.

2. Use ip_dev_find() and ip6_dev_find() to lookup network interfaces

with matching IPv4 and IPv6 addresses, respectivly.

3. In addr_resolve() make sure the "ifa" pointer is always set, also when

the "ifp" is NULL. Else a NULL pointer access might happen trying to
read from the "ifa" pointer later on.

Sponsored by: Mellanox Technologies