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/tbf.h b/src/tbf.h
index adb7dcc..0389595 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -523,6 +523,8 @@
 		struct gprs_rlc_data *block,
 		uint8_t *data, const uint8_t block_idx);
 
+	void egprs_calc_ulwindow_size();
+
 	void update_coding_scheme_counter_ul(const GprsCodingScheme cs);
 
 	/* Please note that all variables here will be reset when changing