restore: networking stack files from reflog (Phases 1-6)

Recovered from reflog commits 1c80937e and d0ecc067 after force-push data loss.
Includes: filter/, icmp_error.rs, slaac.rs, bond.rs, bridge.rs, gre.rs, ipip.rs,
qdisc.rs, tun.rs, vlan.rs, vxlan.rs, netfilter.rs, tun.rs, conntrack.rs, nat.rs,
rule.rs, table.rs, redbear-ufw/, dhcpv6d/, netdiag/ — 39 files total.

netstack/src/scheme/socket.rs

@@ -251,17 +251,24 @@ where
         flags: usize,
     ) -> SyscallResult<usize>;
 
-    fn get_sock_opt(
+fn get_sock_opt(
         &self,
         file: &SchemeFile<Self>,
         name: usize,
         buf: &mut [u8],
     ) -> SyscallResult<usize> {
-        // Return Err for default implementation
+        Err(SyscallError::new(syscall::ENOPROTOOPT))
+    }
+
+    fn set_sock_opt(
+        &mut self,
+        _file: &SchemeFile<Self>,
+        _name: usize,
+        _buf: &[u8],
+    ) -> SyscallResult<usize> {
         Err(SyscallError::new(syscall::ENOPROTOOPT))
     }
 }
-
 pub enum Handle<SocketT>
 where
     SocketT: SchemeSocket,
@@ -453,10 +460,20 @@ where
             // SocketCall::Bind => self.handle_bind(id, &payload),
             // SocketCall::Connect => self.handle_connect(id, &payload),
             SocketCall::SetSockOpt => {
-                // currently not used
-                // self.handle_setsockopt(id, metadata[1] as i32, &payload)
-                // TODO: SO_REUSEADDR from null socket
-                Ok(0)
+                let handle = self.handles.get(fd)?;
+                match handle {
+                    Handle::File(file) => {
+                        let mut socket_set = self.socket_set.borrow_mut();
+                        let socket = socket_set.get_mut::<SocketT>(file.socket_handle());
+                        SocketT::set_sock_opt(
+                            socket,
+                            file,
+                            metadata[1] as usize,
+                            payload,
+                        )
+                    }
+                    _ => Err(SyscallError::new(syscall::ENOPROTOOPT)),
+                }
             }
             SocketCall::GetSockOpt => {
                 let handle = self.handles.get_mut(fd)?;