fusefs: add more checks for buggy FUSE servers

• If a FUSE file system is NFS-exported (either by a kernel or userspace NFS server), then it must support FUSE_LOOKUP operations for ".". But if the response reports a different nodeid than the request, that's very bad. Fail the operation and warn the operator.

• In general, a FUSE file may have a distinct "nodeid" and "inode number". But it the file system is NFS-exported (either by a kernel or userspace NFS server), then those two must match, because the NFS server will do VFS_VGET operations using the inode number. If they don't match, warn the operator.

MFC after: 2 weeks
Sponsored by: ConnectWise
Differential Revision: https://reviews.freebsd.org/D48471