netlink: pass NLMSG_DONE messages to family specific payload decoders

netlink: pass NLMSG_DONE messages to family specific payload decoders

While many NLMSG_DONE messages indeed have payload containing
just one integer, there are exceptions. Handle this by passing
payloads of NLMSG_DONE messages to family specific netlink
payload decoders.

* netlink.c (print_nlmsghdr): Do not skip family detection
for nlmsg_type == NLMSG_DONE.
(decode_nlmsg_type): Skip family specific type decoders
for type == NLMSG_DONE.
(decode_nlmsg_flags): Skip family specific decoding of flags
for type == NLMSG_DONE.
(decode_netlink_sock_diag): Skip for nlmsg_type == NLMSG_DONE.