Unify BTS into a C usable structure

Previous work on BTS class started to get stuff out of the C++ struct
 into a C struct (BTS -> struct gprs_glcmac_bts) so that some parts of
it were accessible from C code. Doing so, however, ended up being messy
too, since all code needs to be switching from one object to another,
which actually refer to the same logical component.

Let's instead rejoin the structures and make sure the struct is
accessible and usable from both C and C++ code by rewriting all methods
to be C compatible and converting 3 allocated suboject as pointers.
This way BTS can internally still use those C++ objects while providing
a clean APi to both C and C++ code.

Change-Id: I7d12c896c5ded659ca9d3bff4cf3a3fc857db9dd
diff --git a/src/poll_controller.h b/src/poll_controller.h
index 65d1fee..8e709a3 100644
--- a/src/poll_controller.h
+++ b/src/poll_controller.h
@@ -21,22 +21,22 @@
 
 #pragma once
 
-struct BTS;
+struct gprs_rlcmac_bts;
 
 /**
  * I belong to a BTS and I am responsible for finding TBFs and
  * SBAs that should have been polled and execute the timeout
  * action on them.
  */
-class PollController {
+struct PollController {
 public:
-	PollController(BTS& bts);
+	PollController(struct gprs_rlcmac_bts& bts);
 
 	/* check for poll timeout */
 	void expireTimedout(int frame_number, unsigned max_delay);
 
 private:
-	BTS& m_bts;
+	struct gprs_rlcmac_bts& m_bts;
 
 private:
 	/* disable copying to avoid slicing */