Implement get network interface by params function in ipoib.

Also fix the validate_ipv4_net_dev() and validate_ipv6_net_dev() functions
which had source and destination addresses swapped, and didn't set the
scope ID for IPv6 link-local addresses.

This allows applications like krping to work using IPoIB devices.

MFC after: 3 days
Approved by: re (gjb)
Sponsored by: Mellanox Technologies