accept MGCP without SDP

SDP is an optional part of MGCP messages. Do not fail when there is no SDP part.

Practically this is useful to compose simpler MGCP responses from TTCN3 tests.
osmo-mgw itself always includes SDP, so there is no real impact on operating
libosmo-mgcp-client with osmo-mgw from osmo-bsc or osmo-msc.

Change-Id: I608001626459ea72415fb142f857550bbb90c683
diff --git a/tests/mgcp_client/mgcp_client_test.c b/tests/mgcp_client/mgcp_client_test.c
index 9c4392f..d2e34a6 100644
--- a/tests/mgcp_client/mgcp_client_test.c
+++ b/tests/mgcp_client/mgcp_client_test.c
@@ -360,7 +360,7 @@
 static struct sdp_section_start_test sdp_section_start_tests[] = {
 	{
 		.body = "",
-		.expect_rc = -EINVAL,
+		.expect_rc = 0,
 	},
 	{
 		.body = "\n\n",
@@ -399,19 +399,19 @@
 		.body = "some mgcp header data\r\nand header params"
 			"\n\r\n"
 			"m=audio 23\r\n",
-		.expect_rc = -EINVAL,
+		.expect_rc = 0,
 	},
 	{
 		.body = "some mgcp header data\r\nand header params"
 			"\r\n\r"
 			"m=audio 23\r\n",
-		.expect_rc = -EINVAL,
+		.expect_rc = 0,
 	},
 	{
 		.body = "some mgcp header data\r\nand header params"
 			"\n\r\r"
 			"m=audio 23\r\n",
-		.expect_rc = -EINVAL,
+		.expect_rc = 0,
 	},
 };