IPv4: Take the socket lock more (fixes TCP connection to localhost)

This fixes an issue where making a TCP connection to localhost didn't
work correctly since the loopback interface is currently synchronous.
(Sending something to localhost would enqueue a packet on the same
interface and then immediately wake the network task to process that
packet.)

This was preventing the TCP handshake from working correctly with
localhost since we'd send out the SYN packet before moving to the
SynSent state. The lock is now held long enough for this operation
to be atomic.

Kernel/Net/IPv4Socket.cpp

@@ -131,6 +131,7 @@ KResult IPv4Socket::bind(Userspace<const sockaddr*> user_address, socklen_t addr
 
 KResult IPv4Socket::listen(size_t backlog)
 {
+    LOCKER(lock());
     int rc = allocate_local_port_if_needed();
     if (rc < 0)
         return KResult(-EADDRINUSE);
@@ -203,6 +204,8 @@ int IPv4Socket::allocate_local_port_if_needed()
 
 KResultOr<size_t> IPv4Socket::sendto(FileDescription&, const UserOrKernelBuffer& data, size_t data_length, int flags, Userspace<const sockaddr*> addr, socklen_t addr_length)
 {
+    LOCKER(lock());
+
     (void)flags;
     if (addr && addr_length != sizeof(sockaddr_in))
         return KResult(-EINVAL);

Kernel/Net/NetworkTask.cpp

@@ -369,6 +369,8 @@ void handle_tcp(const IPv4Packet& ipv4_packet, const timeval& packet_timestamp)
         return;
     }
 
+    LOCKER(socket->lock());
+
     ASSERT(socket->type() == SOCK_STREAM);
     ASSERT(socket->local_port() == tcp_packet.destination_port());
 
@@ -401,6 +403,7 @@ void handle_tcp(const IPv4Packet& ipv4_packet, const timeval& packet_timestamp)
                 klog() << "handle_tcp: couldn't create client socket";
                 return;
             }
+            LOCKER(client->lock());
 #ifdef TCP_DEBUG
             klog() << "handle_tcp: created new client socket with tuple " << client->tuple().to_string().characters();
 #endif

Kernel/Net/Socket.cpp

@@ -244,6 +244,7 @@ KResultOr<size_t> Socket::write(FileDescription& description, size_t, const User
 
 KResult Socket::shutdown(int how)
 {
+    LOCKER(lock());
     if (type() == SOCK_STREAM && !is_connected())
         return KResult(-ENOTCONN);
     if (m_role == Role::Listener)

Kernel/Net/TCPSocket.cpp

@@ -368,6 +368,8 @@ KResult TCPSocket::protocol_listen()
 
 KResult TCPSocket::protocol_connect(FileDescription& description, ShouldBlock should_block)
 {
+    Locker locker(lock());
+
     auto routing_decision = route_to(peer_address(), local_address());
     if (routing_decision.is_zero())
         return KResult(-EHOSTUNREACH);
@@ -388,8 +390,10 @@ KResult TCPSocket::protocol_connect(FileDescription& description, ShouldBlock sh
     m_direction = Direction::Outgoing;
 
     if (should_block == ShouldBlock::Yes) {
+        locker.unlock();
         if (Thread::current()->block<Thread::ConnectBlocker>(nullptr, description).was_interrupted())
             return KResult(-EINTR);
+        locker.lock();
         ASSERT(setup_state() == SetupState::Completed);
         if (has_error()) {
             m_role = Role::None;
@@ -458,6 +462,7 @@ void TCPSocket::shut_down_for_writing()
 
 KResult TCPSocket::close()
 {
+    Locker socket_locker(lock());
     auto result = IPv4Socket::close();
     if (state() == State::CloseWait) {
 #ifdef TCP_SOCKET_DEBUG