misc: Do not mix struct/class in the forward declaration

src/poll_controller.h

@@ -23,7 +23,7 @@
 
 struct gprs_rlcmac_bts;
 
-class BTS;
+struct BTS;
 
 /**
  * I belong to a BTS and I am responsible for finding TBFs and

src/rlc.h

@@ -25,7 +25,7 @@
 #define RLC_MAX_WS  64 /* max window size */
 #define RLC_MAX_LEN 54 /* CS-4 including spare bits */
 
-class BTS;
+struct BTS;
 struct gprs_rlc_v_n;
 
 /* The state of a BSN in the send/receive window */

src/sba.h

@@ -26,7 +26,7 @@ extern "C" {
 #include <osmocom/core/linuxlist.h>
 }
 
-class BTS;
+struct BTS;
 class PollController;
 struct gprs_rlcmac_sba;
 struct gprs_rlcmac_pdch;