test_etcp_router: fix flaky keepalive timeout under dummynet congestion

Root cause: 80kbps congestion causes 9+ second backpressure during push
phase. No packets reach server → keepalive timeout (2s default) fires
→ ETCP link down → BGP cleanup → etcp_router_conn_restart()
  - frees send_q (up to 64 = ROUTER_MAX_SEND_Q_PACKETS lost)
  - sends 9-byte restart notification to service handler (conn=NULL)
  - resets seq to 0

Fixes:
1. Set keepalive_timeout=60000, keepalive_adaptive=0 in test configs
   to prevent spurious timeouts during intentional congestion testing
2. Handle 9-byte restart notification in srv_handler:
   when conn==NULL && len==9 → reset g_expected_seq=0 gracefully

tests/test_etcp_router.c

@@ -169,6 +169,8 @@ static void write_configs(void) {
         "my_public_key=%s\n"
         "tun_ip=10.99.0.1/24\n"
         "tun_ifname=tun99\n"
+        "keepalive_timeout=60000\n"
+        "keepalive_adaptive=0\n"
         "[server: s1]\n"
         "addr=127.0.0.1:%d\n"
         "type=public\n"
@@ -188,6 +190,8 @@ static void write_configs(void) {
         "my_public_key=%s\n"
         "tun_ip=10.99.0.2/24\n"
         "tun_ifname=tun98\n"
+        "keepalive_timeout=60000\n"
+        "keepalive_adaptive=0\n"
         "[server: s1]\n"
         "addr=127.0.0.1:%d\n"
         "type=public\n"
@@ -242,9 +246,15 @@ static int send_one_pkt(uint32_t seq, int data_len) {
 
 // ======================== Server handler ========================
 static void srv_handler(struct ETCP_CONN* conn, struct ll_entry* entry) {
-    (void)conn;
+    // Restart notification: conn=NULL, len=9, format [svc_id:1][node_id:8]
+    if (!conn && entry && entry->dgram && entry->len == 9) {
+        DEBUG_DEBUG(DEBUG_CATEGORY_DEBUG, "srv_handler: restart notification, resetting expected_seq from %u to 0", g_expected_seq);
+        g_expected_seq = 0;
+        queue_dgram_free(entry); queue_entry_free(entry);
+        return;
+    }
     if (!entry || !entry->dgram || entry->len < 10) {
-        printf("[FAIL] srv_handler: bad entry len=%zu\n", entry ? entry->len : 0);
+        printf("[FAIL] srv_handler: bad entry len=%zu conn=%p\n", entry ? entry->len : 0, (void*)conn);
         if (entry) { queue_dgram_free(entry); queue_entry_free(entry); }
         g_fail = 4; g_done = -1;
         return;