tipc: add support for connect() on dgram/rdm sockets

Following the example of ip4_datagram_connect, we store the
address in the socket structure for dgram/rdm sockets and use
that as the default destination for subsequent send() calls.
It is allowed to connect to any address types, and the behaviour
of send() will be the same as a normal sendto() with this address
provided. Binding to an AF_UNSPEC address clears the association.

Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>