tipc: fix bug in bundled buffer reception

In commit ec8a2e56

 ("tipc: same receive
code path for connection protocol and data messages") we omitted the
the possiblilty that an arriving message extracted from a bundle buffer
may be a multicast message. Such messages need to be to be delivered to
the socket via a separate function, tipc_sk_mcast_rcv(). As a result,
small multicast messages arriving as members of a bundle buffer will be
silently dropped.

This commit corrects the error by considering this case in the function
tipc_link_bundle_rcv().

Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>