add BSSLAP coding for Location Services

BSSLAP: there are APDUs transferred in BSSMAP-LE Connection Oriented
Information messages on Lb between BSC and SMLC.
Add BSSLAP coding for these APDU messages:
- TA Layer3
- TA Request
- TA Response, possibly containing Location Estimate coded in GAD
- Reject
- Reset (for intra-BSS handover during TA Request)
- Abort (for inter-BSS handover)

Add encoding and decoding tests.

Change-Id: I6409c4bcac402dc7626a3afce9081c59cd715fe8
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index a31f73a..257c3fa 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -705,6 +705,10 @@
 osmo_nri_ranges_to_str_buf;
 osmo_nri_ranges_to_str_c;
 
+osmo_bsslap_enc;
+osmo_bsslap_dec;
+osmo_bsslap_msgt_names;
+
 osmo_gad_enc;
 osmo_gad_dec;
 osmo_gad_to_str_buf;