Generate SI2ter Rest Octets

Previously we simply omitted SI2ter Rest Octets which is spec violation
which lead to 'Malformed Packet' error in Wireshark RSL dissector. Fix
this by generating empty 'no rest octets' with proper padding. Adjust
test output accordingly.

Change-Id: Ie4419aaaf93a462f501f8d8f7bf2677d37c58f94
Fixes: OS#2711
diff --git a/include/osmocom/bsc/rest_octets.h b/include/osmocom/bsc/rest_octets.h
index 876e0ab..ba25b6d 100644
--- a/include/osmocom/bsc/rest_octets.h
+++ b/include/osmocom/bsc/rest_octets.h
@@ -9,6 +9,7 @@
 /* generate SI1 rest octets */
 int rest_octets_si1(uint8_t *data, uint8_t *nch_pos, int is1800_net);
 int rest_octets_si2quater(uint8_t *data, struct gsm_bts *bts);
+int rest_octets_si2ter(uint8_t *data);
 int rest_octets_si6(uint8_t *data, bool is1800_net);
 
 struct gsm48_si_selection_params {