netinet/tcp.h: add tcp_diag_md5sig struct from linux v4.14

for querying tcp md5 signing keys.
new in linux commit c03fa9bcacd9ac04595cc13f34f3445f0a5ecf13

include/netinet/tcp.h

@@ -220,6 +220,14 @@ struct tcp_md5sig {
 	uint8_t tcpm_key[TCP_MD5SIG_MAXKEYLEN];
 };
 
+struct tcp_diag_md5sig {
+	uint8_t tcpm_family;
+	uint8_t tcpm_prefixlen;
+	uint16_t tcpm_keylen;
+	uint32_t tcpm_addr[4];
+	uint8_t tcpm_key[TCP_MD5SIG_MAXKEYLEN];
+};
+
 struct tcp_repair_window {
 	uint32_t snd_wl1;
 	uint32_t snd_wnd;