mount: Fix -t in listing mode when run as non-root

Presently, libmount-mount completely prohibits the use of -t by non-root
users.  This breaks using -t in listing mode as a user, which represents
a regression against mount-deprecated, macosx and presumably *BSD.

This commit fixes the issue by deferring the mnt_context_is_restricted
check for -t until we know we're not in listing mode.

Signed-off-by: Rich Tollerton <rich.tollerton@ni.com>