Reject invalid hints early in order to not cause a kernel
WARN later if they're restored to or similar.

Reported-by:  <syzbot+d451401ffd00a60677ee@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=d451401ffd00a60677ee
Link: https://lore.kernel.org/r/20200819084648.13956-1-johannes@sipsolutions.net


Signed-off-by: Johannes Berg <johannes.berg@intel.com>