net/smc: support extended GID in SMC-D lgr netlink attribute

Virtual ISM devices introduced in SMCv2.1 requires a 128 bit extended
GID vs. the existing ISM 64bit GID. So the 2nd 64 bit of extended GID
should be included in SMC-D linkgroup netlink attribute as well.

Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>