Update VXLANTest destination port number

Based on RFC 7348, the default IANA-assigned destination UDP port number
for VXLAN is 4789, not the source port number. Update the value in the
VXLANTest class to align with the RFC.

The VXLAN implementation still allows for the destination port number to
be configurable to allow interoperability (as specified by the RFC),
such as with the Linux kernel's default value of 8472.

Signed-off-by: James Raphael Tiovalen <jamestiotio@gmail.com>

tests/src/vxlan_test.cpp

@@ -34,8 +34,8 @@ const uint8_t VXLANTest::expected_packet[PACKET_SIZE] = {
 };
 
 const uint8_t VXLANTest::flags = 8;
-const uint16_t VXLANTest::dport = 19627;
-const uint16_t VXLANTest::sport = 4789;
+const uint16_t VXLANTest::dport = 4789;
+const uint16_t VXLANTest::sport = 19627;
 const uint16_t VXLANTest::p_type = 0xd0ab;
 const small_uint<24> VXLANTest::vni = 0xffffff;
 const IP::address_type VXLANTest::dst_ip = IP::address_type{"2.2.2.2"};
@@ -83,7 +83,11 @@ TEST_F(VXLANTest, ConstructorFromBuffer) {
 
 TEST_F(VXLANTest, OuterUDP) {
     auto pkt = IP{dst_ip, src_ip} / UDP{dport, sport} / VXLAN{expected_packet, PACKET_SIZE};
-    auto const vxlan = pkt.find_pdu<VXLAN>();
+    auto const udp = pkt.find_pdu<UDP>();
+    ASSERT_TRUE(udp != nullptr);
+    EXPECT_EQ(udp->dport(), dport);
+    EXPECT_EQ(udp->sport(), sport);
+    auto const vxlan = udp.find_pdu<VXLAN>();
     ASSERT_TRUE(vxlan != nullptr);
     EXPECT_EQ(vxlan->get_flags(), flags);
     EXPECT_EQ(vxlan->get_vni(), vni);