LU-18828 lnet: lnetctl SIGSEGV in infra_ping_nid

LU-18828 lnet: lnetctl SIGSEGV in infra_ping_nid

Return value of strtok() not checked.
Save error code and continue pinging after syntax error.

Test-Parameters: trivial
Signed-off-by: Frank Sehr <fsehr@whamcloud.com>
Change-Id: I817d7c46ced9e8ea42a283b6c05dfc17ce8781f3
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58460
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>