Add function to properly encode RAI

Add gsm48_encode_ra() which takes appropriate struct as [out] parameter
instead of generic buffer. Using uint8_t buffer instead of proper struct
type prooved to be error-prone - see Coverity CID57877, CID57876.

Old gsm48_construct_ra() is made into tiny wrapper around new
function. The test output is adjusted because of the change in function
return value which was constant and hence ignored anyway.

Related: OS#1640
Change-Id: I31f9605277f4945f207c2c44ff82e62399f8db74
diff --git a/src/gb/libosmogb.map b/src/gb/libosmogb.map
index 9a0dba5..83a3621 100644
--- a/src/gb/libosmogb.map
+++ b/src/gb/libosmogb.map
@@ -9,6 +9,7 @@
 bssgp_msgb_alloc;
 bssgp_msgb_copy;
 bssgp_msgb_tlli_put;
+bssgp_msgb_ra_put;
 bssgp_parse_cell_id;
 bssgp_tx_bvc_block;
 bssgp_tx_bvc_reset;