nbt_server: redirect incoming response packets to the correct interface

nbt_server: redirect incoming response packets to the correct interface

We may send requests packets (WACK challenges or similar things)
via a different udp socket than the socket we receive the
matching response. We need to setup an unexpected handler
on the nbt sockets and redirect responses to the correct
nbt_socket. (By redirect I mean we use the correct
nbt_socket structure, we're *not* resending the packet
with sendto() via the kernel...)

metze
(from samba4wins tree 7ce8e705e5a9aabb787d17fbec7a078d9d6780dc)