GSM 04.08: Add support for parsing CSD related bearer capabilities

Also adds a test case for both encoder and decoder of this IE
diff --git a/include/osmocom/gsm/protocol/gsm_04_08.h b/include/osmocom/gsm/protocol/gsm_04_08.h
index 5057ada..7c558ce 100644
--- a/include/osmocom/gsm/protocol/gsm_04_08.h
+++ b/include/osmocom/gsm/protocol/gsm_04_08.h
@@ -1246,6 +1246,71 @@
 	GSM48_BCAP_RRQ_DUAL_FR	= 3,
 };
 
+/* GSM 04.08 Bearer Capability: Rate Adaption */
+enum gsm48_bcap_ra {
+	GSM48_BCAP_RA_NONE	= 0,
+	GSM48_BCAP_RA_V110_X30	= 1,
+	GSM48_BCAP_RA_X31	= 2,
+	GSM48_BCAP_RA_OTHER	= 3,
+};
+
+/* GSM 04.08 Bearer Capability: Signalling access protocol */
+enum gsm48_bcap_sig_access {
+	GSM48_BCAP_SA_I440_I450	= 1,
+	GSM48_BCAP_SA_X21	= 2,
+	GSM48_BCAP_SA_X28_DP_IN	= 3,
+	GSM48_BCAP_SA_X28_DP_UN	= 4,
+	GSM48_BCAP_SA_X28_NDP	= 5,
+	GSM48_BCAP_SA_X32	= 6,
+};
+
+/* GSM 04.08 Bearer Capability: User Rate */
+enum gsm48_bcap_user_rate {
+	GSM48_BCAP_UR_300	= 1,
+	GSM48_BCAP_UR_1200	= 2,
+	GSM48_BCAP_UR_2400	= 3,
+	GSM48_BCAP_UR_4800	= 4,
+	GSM48_BCAP_UR_9600	= 5,
+	GSM48_BCAP_UR_12000	= 6,
+	GSM48_BCAP_UR_1200_75	= 7,
+};
+
+/* GSM 04.08 Bearer Capability: Parity */
+enum gsm48_bcap_parity {
+	GSM48_BCAP_PAR_ODD	= 0,
+	GSM48_BCAP_PAR_EVEN	= 2,
+	GSM48_BCAP_PAR_NONE	= 3,
+	GSM48_BCAP_PAR_ZERO	= 4,
+	GSM48_BCAP_PAR_ONE	= 5,
+};
+
+/* GSM 04.08 Bearer Capability: Intermediate Rate */
+enum gsm48_bcap_interm_rate {
+	GSM48_BCAP_IR_8k	= 2,
+	GSM48_BCAP_IR_16k	= 3,
+};
+
+/* GSM 04.08 Bearer Capability: Transparency */
+enum gsm48_bcap_transp {
+	GSM48_BCAP_TR_TRANSP	= 0,
+	GSM48_BCAP_TR_RLP	= 1,
+	GSM48_BCAP_TR_TR_PREF	= 2,
+	GSM48_BCAP_TR_RLP_PREF	= 3,
+};
+
+/* GSM 04.08 Bearer Capability: Modem Type */
+enum gsm48_bcap_modem_type {
+	GSM48_BCAP_MT_NONE	= 0,
+	GSM48_BCAP_MT_V21	= 1,
+	GSM48_BCAP_MT_V22	= 2,
+	GSM48_BCAP_MT_V22bis	= 3,
+	GSM48_BCAP_MT_V23	= 4,
+	GSM48_BCAP_MT_V26ter	= 5,
+	GSM48_BCAP_MT_V32	= 6,
+	GSM48_BCAP_MT_UNDEF	= 7,
+	GSM48_BCAP_MT_AUTO_1	= 8,
+};
+
 #define GSM48_TMSI_LEN	5
 #define GSM48_MID_TMSI_LEN	(GSM48_TMSI_LEN + 2)
 #define GSM48_MI_SIZE 32