pdch/tbf: Move gprs_rlcmac_rcv_data_block_acknowledged into the pdch

Move the method into the PDCH. Extract the finding of TLLI into a
new class called Decoding. Move the assemble and forward LLC frames
into the TBF as it is poking in the internals of the TBF.
diff --git a/src/tbf.h b/src/tbf.h
index 0441096..10bff14 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -96,6 +96,9 @@
 	struct msgb *llc_dequeue(bssgp_bvc_ctx *bctx);
 	void update_llc_frame(struct msgb *msg);
 
+	/* TODO: extract LLC class? */
+	int assemble_forward_llc(uint8_t *data, uint8_t len);
+
 	int rlcmac_diag();
 
 	struct llist_head list;