Revision 346141

fusefs: Handle ENOSYS for all remaining opcodes

For many FUSE opcodes, an error of ENOSYS has special meaning.  fusefs
already handled some of those; this commit adds handling for the remainder:

* FUSE_FSYNC, FUSE_FSYNCDIR: ENOSYS means "success, and automatically return
  success without calling the daemon from now on"
* All extattr operations: ENOSYS means "fail EOPNOTSUPP, and automatically
  do it without calling the daemon from now on"

PR:		236557
Sponsored by:	The FreeBSD Foundation