test: Fix the tcp-accept-stress test

It was previously asserted that each thread received at least one connection,
but this is not guaranteed to always be the case due to scheduling. This test
also deadlocked on failure due to a lingering reference to the sending half of
the channel, so that reference is now also eagerly dropped so the test can fail
properly if something bad happens.

Closes #16872

src/test/run-pass/tcp-accept-stress.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// ignore-macos #16872 spurious deadlock
-
 #![feature(phase)]
 
 #[phase(plugin)]
@@ -49,11 +47,9 @@ fn test() {
         let tx = tx.clone();
         spawn(proc() {
             let mut a = a;
-            let mut mycnt = 0u;
             loop {
                 match a.accept() {
                     Ok(..) => {
-                        mycnt += 1;
                         if cnt.fetch_add(1, atomic::SeqCst) == N * M - 1 {
                             break
                         }
@@ -62,7 +58,6 @@ fn test() {
                     Err(e) => fail!("{}", e),
                 }
             }
-            assert!(mycnt > 0);
             tx.send(());
         });
     }
@@ -77,6 +72,7 @@ fn test() {
             tx.send(());
         });
     }
+    drop(tx);
 
     // wait for senders
     assert_eq!(rx.iter().take(N).count(), N);