Fix typo in src/libstd/net/udp.rs doc comment

Affect is usually used as a verb, effect as a verb.

Author: Indy2222

src/libstd/net/udp.rs

@@ -422,7 +422,7 @@ impl UdpSocket {
     /// Sets the value of the `IP_MULTICAST_LOOP` option for this socket.
     ///
     /// If enabled, multicast packets will be looped back to the local socket.
-    /// Note that this may not have any affect on IPv6 sockets.
+    /// Note that this may not have any effect on IPv6 sockets.
     ///
     /// # Examples
     ///
@@ -464,7 +464,7 @@ impl UdpSocket {
     /// this socket. The default value is 1 which means that multicast packets
     /// don't leave the local network unless explicitly requested.
     ///
-    /// Note that this may not have any affect on IPv6 sockets.
+    /// Note that this may not have any effect on IPv6 sockets.
     ///
     /// # Examples
     ///