Caches allocated by the cache manager must be freed again when the cache
manager itself is freed. However, the netlink socket is allocated
indepdently so it should not be freed.
Fixes an off-by-one when releasing local ports. Fixes nl_connect()
to properly close the socket upon failure. Return EBADFD if
operations are performed on unconnected sockets where appropriate.
Makes nl_handle_alloc() return an error if all local ports are
used up.
Thomas Graf