[EventEngine] Fix PosixEventEngine IPv4 support (#32574)

This fixes a bug where connections cannot be made in IPv4-only
environments. To test, hard-code `IsIpv6LoopbackAvailable` to return
false.

Example Error:
`
D0309 00:29:49.514359445 235 tcp_client.cc:67] (event_engine)
EventEngine::Connect Status: INTERNAL: socket: Address family not
supported by protocol
`

This can also be reproduced in gRPC's benchmark environment, which does
not have IPv6 enabled.

src/core/lib/event_engine/posix_engine/tcp_socket_utils.cc

@@ -140,6 +140,11 @@ absl::Status PrepareTcpClientSocket(PosixSocketWrapper sock,
   return absl::OkStatus();
 }
 
+bool SetSocketDualStack(int fd) {
+  const int off = 0;
+  return 0 == setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &off, sizeof(off));
+}
+
 #endif  // GRPC_POSIX_SOCKET_UTILS_COMMON
 
 }  // namespace
@@ -620,11 +625,6 @@ absl::Status PosixSocketWrapper::ApplySocketMutatorInOptions(
   return SetSocketMutator(usage, options.socket_mutator);
 }
 
-bool PosixSocketWrapper::SetSocketDualStack() {
-  const int off = 0;
-  return 0 == setsockopt(fd_, IPPROTO_IPV6, IPV6_V6ONLY, &off, sizeof(off));
-}
-
 bool PosixSocketWrapper::IsIpv6LoopbackAvailable() {
   static bool kIpv6LoopbackAvailable = []() -> bool {
     int fd = socket(AF_INET6, SOCK_STREAM, 0);
@@ -700,19 +700,18 @@ absl::StatusOr<PosixSocketWrapper> PosixSocketWrapper::CreateDualStackSocket(
       newfd = -1;
       errno = EAFNOSUPPORT;
     }
-    if (newfd < 0) {
-      return ErrorForFd(newfd, addr);
-    }
-    PosixSocketWrapper sock(newfd);
     // Check if we've got a valid dualstack socket.
-    if (sock.SetSocketDualStack()) {
+    if (newfd > 0 && SetSocketDualStack(newfd)) {
       dsmode = PosixSocketWrapper::DSMode::DSMODE_DUALSTACK;
-      return sock;
+      return PosixSocketWrapper(newfd);
     }
     // If this isn't an IPv4 address, then return whatever we've got.
     if (!ResolvedAddressIsV4Mapped(addr, nullptr)) {
+      if (newfd <= 0) {
+        return ErrorForFd(newfd, addr);
+      }
       dsmode = PosixSocketWrapper::DSMode::DSMODE_IPV6;
-      return sock;
+      return PosixSocketWrapper(newfd);
     }
     // Fall back to AF_INET.
     if (newfd >= 0) {
@@ -834,10 +833,6 @@ absl::Status PosixSocketWrapper::ApplySocketMutatorInOptions(
   grpc_core::Crash("unimplemented");
 }
 
-bool PosixSocketWrapper::SetSocketDualStack() {
-  grpc_core::Crash("unimplemented");
-}
-
 bool PosixSocketWrapper::IsSocketReusePortSupported() {
   grpc_core::Crash("unimplemented");
 }

src/core/lib/event_engine/posix_engine/tcp_socket_utils.h

@@ -238,9 +238,6 @@ class PosixSocketWrapper {
     DSMODE_DUALSTACK
   };
 
-  // Tries to set the socket to dualstack. Returns true on success.
-  bool SetSocketDualStack();
-
   // Returns the underlying file-descriptor.
   int Fd() const { return fd_; }