iuup_cn_node.c: use correct header for AMR SID frames

rx_data(): if iuup header (4 bytes) + amr payload (5 bytes) is 9 bytes
then it means that this is AMR SID (Comfort Noise Frame) and other
header should be used. The second byte of AMR header is set to 0x44.
diff --git a/tests/iuup/iuup_test.c b/tests/iuup/iuup_test.c
index e6f2ca5..6144ac8 100644
--- a/tests/iuup/iuup_test.c
+++ b/tests/iuup/iuup_test.c
@@ -116,6 +116,13 @@
 	       msgb_from_hex("IuUP-Data",
 			     RTP_HEADER IUUP_HEADER RTP_PAYLOAD));
 
+	printf("\nReceive payload encapsulated in IuUP. Expecting rx_payload() of just RTP packet\n");
+	printf("i.e. should strip away " "0401479e" "\n");
+	expect_rx_payload = RTP_HEADER "f044" "26e9b851ee";
+	rx_pdu(cn,
+	       msgb_from_hex("IuUP-Data",
+			     RTP_HEADER "0401479e" "26e9b851ee"));
+
 	printf("\nTransmit RTP. Expecting tx_msg() with inserted IuUP header\n");
 	expect_tx_msg = RTP_HEADER "000002b3" RTP_PAYLOAD;
 	tx_payload(cn,