net/smc: use the retry mechanism for netlink messages

When the netlink messages to be sent to the userspace
are too big for a single netlink message, send them in
chunks using the netlink_dump infrastructure. Modify the
smc diag dump code so that it can signal to the netlink_dump
infrastructure that it needs to send more data.

Signed-off-by: Guvenc Gulce <guvenc@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>