smc: ETH_ALEN as memcpy length for mac addresses

When creating an SMC connection, there is a CLC (connection layer control)
handshake to prepare for RDMA traffic. The corresponding code is part of
commit 0cfdd8f9 ("smc: connection and link group creation").
Mac addresses to be exchanged in the handshake are copied with a wrong
length of 12 instead of 6 bytes. Following code overwrites the wrongly
copied code, but nevertheless the correct length should already be used for
the preceding mac address copying. Use ETH_ALEN for the memcpy length with
mac addresses.

Signed-off-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Fixes: 0cfdd8f9 ("smc: connection and link group creation")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>