LU-14296 lnet: use an unbound cred in kiblnd_resolve_addr()

In kiblnd_resolve_addr() call prepare_kernel_cred(NULL) rather than
prepare_creds() to get a cred with unbound capabilities.

Fixes: 1e4bd16acfa ("LU-14006 o2ib: raise bind cap before resolving address")
Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: Ib2500d82aa4eab5590fa95ae73fd75b2ab542bcd
Reviewed-on: https://review.whamcloud.com/41137
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>