net/smc: add ipv6 support to CLC layer

The CLC layer is updated to support ipv6 proposal messages from peers and
to match incoming proposal messages against the ipv6 addresses of the net
device. struct smc_clc_ipv6_prefix is updated to provide the space for an
ipv6 address (struct was not used before). SMC_CLC_MAX_LEN is updated to
include the size of the proposal prefix. Existing code in net is not
affected, the previous SMC_CLC_MAX_LEN value is large enough to hold ipv4
proposal messages.

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