Fix error message when one side of unix sockets is closed for writing.

When one end of the connection is closed, write for unix sockets returns
connection refused error in Linux. Make the gVisor behavior the same as Linux.

PiperOrigin-RevId: 631949102

pkg/sentry/socket/unix/unix.go

@@ -351,6 +351,12 @@ func (s *Socket) Write(ctx context.Context, src usermem.IOSequence, opts vfs.Wri
 	if w.Notify != nil {
 		w.Notify()
 	}
+	if _, skType, _ := s.Type(); skType == linux.SOCK_DGRAM {
+		if err != nil && err.Error() == linuxerr.EPIPE.Error() {
+			log.Infof("HERE....")
+			return n, linuxerr.ECONNREFUSED
+		}
+	}
 	return n, err
 
 }

test/syscalls/linux/socket_unix_dgram.cc

@@ -30,10 +30,6 @@ namespace testing {
 namespace {
 
 TEST_P(DgramUnixSocketPairTest, WriteOneSideClosed) {
-  // FIXME(b/35925052): gVisor datagram sockets return EPIPE instead of
-  // ECONNREFUSED.
-  SKIP_IF(IsRunningOnGvisor());
-
   auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
   ASSERT_THAT(close(sockets->release_first_fd()), SyscallSucceeds());
   constexpr char kStr[] = "abc";