LU-18535 ptlrpc: do not use kstrndup()

LU-18535 ptlrpc: do not use kstrndup()

instead use OBD_ALLOC() + memcpy() so subsequent OBD_FREE() does
correct math to detect memory leaks.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Ib6ab1ec865f3d1c9e92328b4ccddef9c1861dee4
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57385
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>