net/smc: Introduce SMCR get linkgroup command

mainline inclusion
from mainline-v5.11-rc1
commit e9b8c845
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I78IFM
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=e9b8c845cb342a3ab3d92235a54d0d1ad06d7204



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Introduce get linkgroup command which loops through
all available SMCR linkgroups. It uses the SMC-R linkgroup
list as entry point, not the socket list, which makes
linkgroup diagnosis possible, in case linkgroup does not
contain active connections anymore.

Signed-off-by: Guvenc Gulce <guvenc@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Yingyu Zeng <zengyingyu@sangfor.com.cn>