Fix overly strict lifetime in TcpSocket.

src/socket/tcp.rs

@@ -1685,8 +1685,8 @@ impl<'a> TcpSocket<'a> {
     }
 }
 
-impl<'a> Into<Socket<'a, 'a>> for TcpSocket<'a> {
-    fn into(self) -> Socket<'a, 'a> {
+impl<'a, 'b> Into<Socket<'a, 'b>> for TcpSocket<'a> {
+    fn into(self) -> Socket<'a, 'b> {
         Socket::Tcp(self)
     }
 }