Add WIP code for SCCP User Adaptation (SUA) and SCCP User SAP

The idea of this code is to
* provide a SCCP User SAP as boundary between the User of SCCP
  or SCCP-like transport like SUA
* implement the minimum subset of SUA to transport RANAP messages
  betweene HNB-GW and MSC/SGSN

At this point
* we don't yet implement the proper state machines and timer
* we don't imp[lement the SCCP RESET procedure
* we don't implement AS/ASP management

The code is full of FIXMEs whihc hopefully will get fixed gradually.

After some cleanup + verification, it should move to a library, possibly
either replacing/renaming libomo-sccp, or adding it to libosmo-netif?
diff --git a/sigtran/sua_test_common.c b/sigtran/sua_test_common.c
new file mode 100644
index 0000000..92c2b38
--- /dev/null
+++ b/sigtran/sua_test_common.c
@@ -0,0 +1,95 @@
+#include "sua_test_common.h"
+
+static const struct log_info_cat log_cat[] = {
+	[DMAIN] = {
+		.name = "DMAIN", .loglevel = LOGL_DEBUG, .enabled = 1,
+		.color = "",
+		.description = "Main program",
+	},
+	[DSUA] = {
+		.name = "DSUA", .loglevel = LOGL_DEBUG, .enabled = 1,
+		.color = "",
+		.description = "SCCP User Adaption",
+	},
+	[DXUA] = {
+		.name = "DXUA", .loglevel = LOGL_DEBUG, .enabled = 1,
+		.color = "",
+		.description = "X User Adaption encoding/decoding",
+	},
+
+};
+
+const struct log_info test_log_info = {
+	.cat = log_cat,
+	.num_cat = ARRAY_SIZE(log_cat),
+};
+
+int tx_unitdata(struct sua_link *link)
+{
+	struct msgb *msg = msgb_alloc(1024, "tx_unitdata");
+	struct osmo_scu_prim *prim;
+	struct osmo_scu_unitdata_param *param;
+	uint8_t *cur;
+
+	prim = (struct osmo_scu_prim *) msgb_put(msg, sizeof(*prim));
+	param = &prim->u.unitdata;
+	param->calling_addr.presence = OSMO_SCCP_ADDR_T_SSN;
+	param->called_addr.presence = OSMO_SCCP_ADDR_T_SSN;
+	osmo_prim_init(&prim->oph, SCCP_SAP_USER, OSMO_SCU_PRIM_N_UNITDATA, PRIM_OP_REQUEST, msg);
+
+	cur = msg->l2h = msgb_put(msg, 3);
+	cur[0] = 1; cur[1] = 2; cur[2] = 3;
+
+	return osmo_osmo_sua_user_link_down(link, &prim->oph);
+}
+
+static void sccp_make_addr_pc_ssn(struct osmo_sccp_addr *addr, uint32_t pc, uint32_t ssn)
+{
+	addr->presence = OSMO_SCCP_ADDR_T_SSN | OSMO_SCCP_ADDR_T_PC;
+	addr->ssn = ssn;
+	addr->pc = pc;
+}
+
+#define SSN_RANAP 142
+
+struct osmo_prim_hdr *make_conn_req(uint32_t conn_id)
+{
+	struct msgb *msg = msgb_alloc(1024, "conn_req");
+	struct osmo_scu_prim *prim;
+
+	prim = (struct osmo_scu_prim *) msgb_put(msg, sizeof(*prim));
+	osmo_prim_init(&prim->oph, SCCP_SAP_USER,
+			OSMO_SCU_PRIM_N_CONNECT,
+			PRIM_OP_REQUEST, msg);
+	/* Set SSN for calling and called addr */
+	sccp_make_addr_pc_ssn(&prim->u.connect.called_addr, 2, SSN_RANAP);
+	sccp_make_addr_pc_ssn(&prim->u.connect.calling_addr, 1, SSN_RANAP);
+	prim->u.connect.sccp_class = 2;
+	prim->u.connect.conn_id = conn_id;
+
+	return &prim->oph;
+}
+
+int tx_conn_req(struct sua_link *link, uint32_t conn_id)
+{
+	struct osmo_prim_hdr *prim = make_conn_req(conn_id);
+	return osmo_osmo_sua_user_link_down(link, prim);
+}
+
+struct osmo_prim_hdr *
+make_dt1_req(uint32_t conn_id, const uint8_t *data, unsigned int len)
+{
+	struct msgb *msg = msgb_alloc(1024, "dt1");
+	struct osmo_scu_prim *prim;
+
+	prim = (struct osmo_scu_prim *) msgb_put(msg, sizeof(*prim));
+	osmo_prim_init(&prim->oph, SCCP_SAP_USER,
+			OSMO_SCU_PRIM_N_DATA,
+			PRIM_OP_REQUEST, msg);
+	prim->u.data.conn_id = conn_id;
+
+	msg->l2h = msgb_put(msg, len);
+	memcpy(msg->l2h, data, len);
+
+	return &prim->oph;
+}