Kernel: Stop exposing gateway field

It doesn't make sense after introduction of routing table which allows
having multiple gateways for every interface, and isn't used by any of
the userspace programs now.

Kernel/GlobalProcessExposed.cpp

@@ -55,10 +55,6 @@ private:
                 auto ipv4_netmask = TRY(adapter.ipv4_netmask().to_string());
                 TRY(obj.add("ipv4_netmask", ipv4_netmask->view()));
             }
-            if (!adapter.ipv4_gateway().is_zero()) {
-                auto ipv4_gateway = TRY(adapter.ipv4_gateway().to_string());
-                TRY(obj.add("ipv4_gateway", ipv4_gateway->view()));
-            }
             TRY(obj.add("packets_in", adapter.packets_in()));
             TRY(obj.add("bytes_in", adapter.bytes_in()));
             TRY(obj.add("packets_out", adapter.packets_out()));

Kernel/Net/NetworkAdapter.cpp

@@ -159,9 +159,4 @@ void NetworkAdapter::set_ipv4_netmask(IPv4Address const& netmask)
     m_ipv4_netmask = netmask;
 }
 
-void NetworkAdapter::set_ipv4_gateway(IPv4Address const& gateway)
-{
-    m_ipv4_gateway = gateway;
-}
-
 }

Kernel/Net/NetworkAdapter.h

@@ -55,7 +55,6 @@ public:
     IPv4Address ipv4_address() const { return m_ipv4_address; }
     IPv4Address ipv4_netmask() const { return m_ipv4_netmask; }
     IPv4Address ipv4_broadcast() const { return IPv4Address { (m_ipv4_address.to_u32() & m_ipv4_netmask.to_u32()) | ~m_ipv4_netmask.to_u32() }; }
-    IPv4Address ipv4_gateway() const { return m_ipv4_gateway; }
     virtual bool link_up() { return false; }
     virtual i32 link_speed()
     {
@@ -66,7 +65,6 @@ public:
 
     void set_ipv4_address(IPv4Address const&);
     void set_ipv4_netmask(IPv4Address const&);
-    void set_ipv4_gateway(IPv4Address const&);
 
     void send(MACAddress const&, ARPPacket const&);
     void fill_in_ipv4_header(PacketWithTimestamp&, IPv4Address const&, MACAddress const&, IPv4Address const&, IPv4Protocol, size_t, u8 type_of_service, u8 ttl);
@@ -103,7 +101,6 @@ private:
     MACAddress m_mac_address;
     IPv4Address m_ipv4_address;
     IPv4Address m_ipv4_netmask;
-    IPv4Address m_ipv4_gateway;
 
     // FIXME: Make this configurable
     static constexpr size_t max_packet_buffers = 1024;

Kernel/Net/NetworkTask.cpp

@@ -67,7 +67,6 @@ void NetworkTask_main(void*)
         if (adapter.class_name() == "LoopbackAdapter"sv) {
             adapter.set_ipv4_address({ 127, 0, 0, 1 });
             adapter.set_ipv4_netmask({ 255, 0, 0, 0 });
-            adapter.set_ipv4_gateway({ 0, 0, 0, 0 });
         }
 
         adapter.on_receive = [&]() {