net/smc: ipv6 support for smc_diag.c

Update smc_diag.c to support ipv6 addresses on the diagnosis interface.

Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>