nfs: fix xattr inode op pointers when disabled

nfs: fix xattr inode op pointers when disabled

Chris Mason reported a NULL pointer derefernence in generic_getxattr()
that was due to sb->s_xattr being NULL.

The reason is that the nfs #ifdef's for ACL support were misplaced, and
the nfs3 inode operations had the xattr operation pointers set up, even
though xattrs were not actually supported.  As a result, the xattr code
was being called without the infrastructure having been set up.

Move the #ifdef's appropriately.

Reported-and-tested-by: Chris Mason <[email protected]>
Acked-by: Al Viro [email protected]>
Signed-off-by: Linus Torvalds <[email protected]>