pcu_if: implement support for 3-digit MNC

Add the mnc_3_digits member to the info_ind.

Instead of changing to e.g. osmo_plmn_id, add the flag separately, and instead
of bool use a uint8_t, to not raise any struct packing issues and clarify the
flag's size beyond any doubt.

Bump the PCU interface version to 9.
This is one part of the three identical pcuif_proto.h patches:
- I49cd762c3c9d7ee6a82451bdf3ffa2a060767947 (osmo-bts)
- I787fed84a7b613158a5618dd5cffafe4e4927234 (osmo-pcu)
- I78f30aef7aa224b2e9db54c3a844d8f520b3aee0 (osmo-bsc)

Depends: Id2240f7f518494c9df6c8bda52c0d5092f90f221 (libosmocore)
Change-Id: I78f30aef7aa224b2e9db54c3a844d8f520b3aee0
diff --git a/src/libbsc/pcu_sock.c b/src/libbsc/pcu_sock.c
index 85af598..caec40d 100644
--- a/src/libbsc/pcu_sock.c
+++ b/src/libbsc/pcu_sock.c
@@ -154,7 +154,7 @@
 	/* RAI */
 	info_ind->mcc = bts->network->plmn.mcc;
 	info_ind->mnc = bts->network->plmn.mnc;
-	/* TODO: plmn.mnc_3_digits */
+	info_ind->mnc_3_digits = bts->network->plmn.mnc_3_digits;
 	info_ind->lac = bts->location_area_code;
 	info_ind->rac = bts->gprs.rac;