ignore errors if an interface can't join multicast

This works okay on my home network, but it's a little more magical than
I wanted - I can't force it to pick up the wifi interface. If the
Ethernet is plugged in, the laptop always and only picks that, even
if I know the server only asked the Ethernet interface.

This is fine, but only because my Ethernet happens to be faster than
my Wifi. I'm not sure how it will behave at work, where WiFi and
Ethernet may be separate networks.

At least the error messages are better now, so I can figure out why
it wasn't auto-starting with systemd.

src/client.rs

@@ -30,7 +30,9 @@ pub async fn client <I : Iterator <Item=String>> (mut args: I) -> Result <(), Ap
 	let socket = UdpSocket::bind (SocketAddrV4::new (Ipv4Addr::UNSPECIFIED, 0)).await?;
 	
 	for bind_addr in bind_addrs {
-		socket.join_multicast_v4 (common_params.multicast_addr, bind_addr)?;
+		if let Err (e) = socket.join_multicast_v4 (common_params.multicast_addr, bind_addr) {
+			println! ("Error joining multicast group with iface {}: {:?}", bind_addr, e);
+		}
 	}
 	
 	let mut idem_id = [0u8; 8];

src/server.rs

@@ -15,7 +15,9 @@ pub async fn server <I: Iterator <Item=String>> (args: I) -> Result <(), AppErro
 	let socket = UdpSocket::bind (SocketAddrV4::new (Ipv4Addr::UNSPECIFIED, params.common.server_port)).await?;
 	
 	for bind_addr in &params.bind_addrs {
-		socket.join_multicast_v4 (params.common.multicast_addr, *bind_addr)?;
+		if let Err (e) = socket.join_multicast_v4 (params.common.multicast_addr, *bind_addr) {
+			println! ("Error joining multicast group with iface {}: {:?}", bind_addr, e);
+		}
 	}
 	
 	serve_interface (params, socket).await?;