nettest: fix doc for testPresentTimeout

Fixes golang/go#30275

Change-Id: I0636326dc5d2b59d0dbdc446c2a424c50a395b2f
Reviewed-on: https://go-review.googlesource.com/c/162923
Reviewed-by: Mikio Hara <mikioh.public.networking@gmail.com>
Run-TryBot: Mikio Hara <mikioh.public.networking@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

nettest/conntest.go

@@ -239,7 +239,7 @@ func testPastTimeout(t *testing.T, c1, c2 net.Conn) {
 	testRoundtrip(t, c1)
 }
 
-// testPresentTimeout tests that a deadline set while there are pending
+// testPresentTimeout tests that a past deadline set while there are pending
 // Read and Write operations immediately times out those operations.
 func testPresentTimeout(t *testing.T, c1, c2 net.Conn) {
 	var wg sync.WaitGroup