feat(server): add service property to server::conn::Parts

This allows getting the original service back.

Closes #1471

Cherry-pick of commit bf7c0bbf4f55fdf465407874b0b2d4bd748e6783 from the
0.11.x branch.

src/client/conn.rs

@@ -354,7 +354,7 @@ where
     ///
     /// Only works for HTTP/1 connections. HTTP/2 connections will panic.
     pub fn into_parts(self) -> Parts<T> {
-        let (io, read_buf) = match self.inner {
+        let (io, read_buf, _) = match self.inner {
             Either::A(h1) => h1.into_inner(),
             Either::B(_h2) => {
                 panic!("http2 cannot into_inner");