net/socket: Use SO_REUSEPORT for server sockets

src/net/socket/tcp_socket_posix.cc

@@ -487,6 +487,17 @@ int TCPSocketPosix::GetPeerAddress(IPEndPoint* address) const {
 
 int TCPSocketPosix::SetDefaultOptionsForServer() {
   DCHECK(socket_);
+
+#ifdef SO_REUSEPORT
+  int reuseport = 1;
+  int rv =
+      setsockopt(socket_->socket_fd(), SOL_SOCKET, SO_REUSEPORT,
+                 reinterpret_cast<const char*>(&reuseport), sizeof(reuseport));
+  // Ignore errors that the option does not exist.
+  if (rv != 0 && errno != ENOPROTOOPT)
+    return MapSystemError(errno);
+#endif  // SO_REUSEPORT
+
   return AllowAddressReuse();
 }