LU-10391 mgs: copy full nid string

LU-10391 mgs: copy full nid string

For IPv6 testing in mgs_steal_client_llog_handler() the full NID
string was not being copied. Instead we copied the size of pointer
not the NID string. Copy the full NID string.

Fixes: c0cb747e ("LU-13306 mgs: use large NIDS in the nid table on the MGS")
Change-Id: I7e19db0b0d3806c1c6fabe2ede0d880a45fe3052
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53115
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Etienne AUJAMES <eaujames@ddn.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>