gsm_08_58: add proprietary IE to signal Repeated ACCH Capability

3GPP TS 24.008, section 10.5.1.7 specifies a Repeated ACCH Capability
bit in the Classmark 3 IE. Unfortunately, there is no way specified how
the Repeated ACCH feature should be controlled on RSL level. Since it is
not unusual that BTS/BSC vendors occassionally add proprietary IEs to
different RSL messages we may pick this as a solution as well and add a
propritary RSL_IE_OSMO_REP_ACCH_CAP IE, so that we can enable repeated
FACCH/SACCH on the BTS side when we send RSL CHAN ACT or RSL CHAN MODE MODIFY
messages.

Change-Id: I61ea6bf54ea90bd69b73ea0f0f3dc19a4214207b
Related: OS#4796 SYS#5114
diff --git a/include/osmocom/gsm/protocol/gsm_08_58.h b/include/osmocom/gsm/protocol/gsm_08_58.h
index cd13a7d..95da23a 100644
--- a/include/osmocom/gsm/protocol/gsm_08_58.h
+++ b/include/osmocom/gsm/protocol/gsm_08_58.h
@@ -337,6 +337,9 @@
 	RSL_IE_SIEMENS_HIGHEST_RATE	= 0x4e,
 	RSL_IE_SIEMENS_SUGGESTED_RATE	= 0x4f,
 
+	/* Osmocom specific */
+	RSL_IE_OSMO_REP_ACCH_CAP= 0x60,
+
 	/* ip.access */
 	RSL_IE_IPAC_SRTP_CONFIG	= 0xe0,
 	RSL_IE_IPAC_PROXY_UDP	= 0xe1,