fuse: export fuse_abi only when fuse is enabled

Co-authored-by: Martin Kröning <mkroening@posteo.net>

Author: cagatay-y

src/fs/mod.rs

@@ -1,5 +1,6 @@
 #[cfg(all(feature = "fuse", feature = "pci"))]
 pub(crate) mod fuse;
+#[cfg(all(feature = "fuse", feature = "pci"))]
 mod fuse_abi;
 mod mem;
 mod uhyve;