Add compression support in EGPRS PUAN

This adds compression of bitmap in PUAN. The compressed bitmap
is used only if the number of bits in the bitmap does not fit in
the message and there is a gain after compression.
The algorithm is part of libosmocore and so there is dependency
on the libosmocore for compilation.
The algorithm is tested on integration setup by forcing compression.

Change-Id: Id2eec4b5eb6da0ebd24054b541b09b700b9b40ba
diff --git a/src/rlc.h b/src/rlc.h
index b2fcd95..7db205d 100644
--- a/src/rlc.h
+++ b/src/rlc.h
@@ -347,6 +347,7 @@
 	bool is_received(uint16_t bsn) const;
 
 	void update_rbb(char *rbb);
+	uint16_t update_egprs_rbb(uint8_t *rbb);
 	void raise_v_r_to(int moves);
 	void raise_v_r(const uint16_t bsn);
 	uint16_t raise_v_q();