LU-17545 lnet: use unsafe_memcpy() when flexible array

LU-17545 lnet: use unsafe_memcpy() when flexible array

To avoid <memcpy: detected field-spanning write (size 64)
of single field "&lp->lp_data->pb_info" at
.../lnet/lnet/peer.c:2456 (size 16)> false positive
msgs/error.

Signed-off-by: Bruno Faccini <bfaccini@nvidia.com>
Change-Id: I4e2fc58e31f60b434a9050393cd65b89c54f0798
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54069
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>