netlink: compatibility with old serve() interface
netlink: add default address for unix sockets
netlink: rewind envelope buffer before encoding
netlink: fix typo
netlink: silently drop routing errors (2B fixed)
netlink: drop responses w/o IPR_ATTR_CDATA (2B fixed)
netlink: proper use of the message type

custom Netlink message type: NLMSG_TRANSPORT
tests: bring back unencrypted remote tests