EXI_DeviceEthernet: Make internal members and functions private

Previously, the entirety of CEXIETHERNET was exposed publically, which
wasn't necessary. We simply make the thread function part of the
internal interface, which gives it access to internal data members,
while keeping everything else outside of it.

Source/Core/Core/HW/EXI/BBA-TAP/TAP_Apple.cpp

@@ -63,7 +63,7 @@ bool CEXIETHERNET::SendFrame(const u8* frame, u32 size)
   }
 }
 
-static void ReadThreadHandler(CEXIETHERNET* self)
+void CEXIETHERNET::ReadThreadHandler(CEXIETHERNET* self)
 {
   while (!self->readThreadShutdown.IsSet())
   {

Source/Core/Core/HW/EXI/BBA-TAP/TAP_Unix.cpp

@@ -125,7 +125,7 @@ bool CEXIETHERNET::SendFrame(const u8* frame, u32 size)
 }
 
 #ifdef __linux__
-static void ReadThreadHandler(CEXIETHERNET* self)
+void CEXIETHERNET::ReadThreadHandler(CEXIETHERNET* self)
 {
   while (!self->readThreadShutdown.IsSet())
   {

Source/Core/Core/HW/EXI/BBA-TAP/TAP_Win32.cpp

@@ -263,7 +263,7 @@ bool CEXIETHERNET::IsActivated()
   return mHAdapter != INVALID_HANDLE_VALUE;
 }
 
-static void ReadThreadHandler(CEXIETHERNET* self)
+void CEXIETHERNET::ReadThreadHandler(CEXIETHERNET* self)
 {
   while (!self->readThreadShutdown.IsSet())
   {

Source/Core/Core/HW/EXI/EXI_DeviceEthernet.h

@@ -210,7 +210,7 @@ public:
   void DMARead(u32 addr, u32 size) override;
   void DoState(PointerWrap& p) override;
 
-  // private:
+private:
   struct
   {
     enum
@@ -312,6 +312,7 @@ public:
   std::unique_ptr<u8[]> tx_fifo;
 
   // TAP interface
+  static void ReadThreadHandler(CEXIETHERNET* self);
   bool Activate();
   void Deactivate();
   bool IsActivated();