fix: HTTP fallback probe when ICMP reports 100% loss (Eyeride NAT blocks ICMP)

Eyeride 5G device passes HTTP traffic but drops ICMP, causing false 100% loss.
When ping gives 100% loss, try curl --interface to confirm connectivity; if
HTTP probe succeeds, correct loss to 0% and derive latency from connect time.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package/kit-busrouter/files/usr/lib/busrouter/telemetry-synology.sh

@@ -239,6 +239,18 @@ _ping_iface() {
 	# Extract loss
 	_loss=$(echo "$_out" | sed -n 's/.* \([0-9]*\)% packet loss.*/\1/p')
 	[ -z "$_loss" ] && _loss="null"
+	# If ICMP reports 100% loss, try HTTP probe — Eyeride NAT blocks ICMP but passes HTTP.
+	if [ "$_loss" = "100" ]; then
+		_t0=$(date +%s%3N 2>/dev/null || date +%s)
+		_hcode=$(curl -s --interface "$_iface" --connect-timeout 5 --max-time 8 \
+			-o /dev/null -w "%{http_code}" http://1.1.1.1 2>/dev/null)
+		_t1=$(date +%s%3N 2>/dev/null || date +%s)
+		if [ -n "$_hcode" ] && [ "$_hcode" != "000" ]; then
+			_loss="0"
+			[ -z "$_avg" ] || [ "$_avg" = "null" ] && \
+				_avg=$(awk "BEGIN { printf \"%.0f\", ${_t1} - ${_t0} }" 2>/dev/null)
+		fi
+	fi
 	printf '%s %s %s\n' "${_avg}" "${_jitter}" "${_loss}" | tr -d '\n\r'
 }