atmodem: Add at_util_get_cgdcont_command

The function at_util_get_cgdcont_command computes the AT+CGDCONT
string, as per 3GPP 27.007.
It uses a second function, at_util_gprs_proto_to_pdp_type,
that returns the pdp_type string for the command

drivers/atmodem/atutil.c

@@ -670,3 +670,30 @@ int at_util_gprs_auth_method_to_auth_prot(
 
 	return 0;
 }
+
+const char *at_util_gprs_proto_to_pdp_type(enum ofono_gprs_proto proto)
+{
+	switch (proto) {
+	case OFONO_GPRS_PROTO_IPV6:
+		return "IPV6";
+	case OFONO_GPRS_PROTO_IPV4V6:
+		return "IPV4V6";
+		break;
+	case OFONO_GPRS_PROTO_IP:
+		return "IP";
+	}
+
+	return NULL;
+}
+
+char *at_util_get_cgdcont_command(guint cid, enum ofono_gprs_proto proto,
+								const char *apn)
+{
+	const char *pdp_type = at_util_gprs_proto_to_pdp_type(proto);
+
+	if (!apn)
+		return g_strdup_printf("AT+CGDCONT=%u", cid);
+
+	return g_strdup_printf("AT+CGDCONT=%u,\"%s\",\"%s\"", cid, pdp_type,
+									apn);
+}

drivers/atmodem/atutil.h

@@ -90,6 +90,19 @@ int at_util_get_ipv4_address_and_netmask(const char *addrnetmask,
 int at_util_gprs_auth_method_to_auth_prot(
 				enum ofono_gprs_auth_method auth_method);
 
+const char *at_util_gprs_proto_to_pdp_type(enum ofono_gprs_proto proto);
+
+/*
+ * at_util_get_cgdcont_command
+ * if the apn pointer is NULL, the context will be removed: the resulting
+ * string will be like: AT+CGDCONT=7
+ * but if apn pointer is not NULL and the string is empty, then
+ * this function will create a normal context with empty apn, like:
+ * AT+CGDCONT=4,"IPV6",""
+ */
+char *at_util_get_cgdcont_command(guint cid, enum ofono_gprs_proto proto,
+							const char *apn);
+
 struct cb_data {
 	void *cb;
 	void *data;