Add IGMP, prepend_buffer/parse_buffer, split UDP header, discovery tests, test all

firmware/include/udp.h

@@ -0,0 +1,29 @@
+#pragma once
+#include <cstdint>
+#include "eth.h"
+#include "ipv4.h"
+
+namespace udp {
+
+struct __attribute__((packed)) header {
+    uint16_t src_port;
+    uint16_t dst_port;
+    uint16_t length;
+    uint16_t checksum;
+};
+static_assert(sizeof(header) == 8);
+
+template <typename Buf>
+void prepend(Buf& buf, const eth::mac_addr& dst_mac, const eth::mac_addr& src_mac,
+             ipv4::ip4_addr src_ip, ipv4::ip4_addr dst_ip,
+             uint16_t src_port, uint16_t dst_port,
+             size_t payload_len, uint8_t ttl = 64) {
+    auto* u = buf.template prepend<header>();
+    u->src_port = src_port;
+    u->dst_port = dst_port;
+    u->length = __builtin_bswap16(sizeof(header) + payload_len);
+    u->checksum = 0;
+    ipv4::prepend(buf, dst_mac, src_mac, src_ip, dst_ip, 17, sizeof(header) + payload_len, ttl);
+}
+
+} // namespace udp