wtp: rework kernel socket handling

Switch to a connected UDP kernel socket. Comparing the
local and remote IPs is no longer required and handling
different IP versions and UDP types is automatic.

The WTP logic needs to reopen the socket on demand now.

src/wtp/wtp_dfa_dtls.c

@@ -39,8 +39,9 @@ void wtp_start_datachannel(void) {
 	}
 #endif
 
-	/* Connect to AC data channel */
-	if (!wtp_kmod_connect(&dataaddr.ss, &g_wtp.sessionid, g_wtp.mtu)) {
+	/* Bind data address and Connect to AC data channel */
+	if (wtp_kmod_bind(g_wtp.net.localaddr.ss.ss_family) ||
+	    !wtp_kmod_connect(&dataaddr.ss, &g_wtp.sessionid, g_wtp.mtu)) {
 		/* Reset AC Prefered List Position */
 		g_wtp.acpreferedselected = 0;