fix: restore CH390 bridge flow and sync driver docs

Drivers/LwIP/src/core/ipv4/etharp.c

@@ -645,7 +645,6 @@ etharp_input(struct pbuf *p, struct netif *netif)
   /* these are aligned properly, whereas the ARP header fields might not be */
   ip4_addr_t sipaddr, dipaddr;
   u8_t for_us, from_us;
-
   LWIP_ASSERT_CORE_LOCKED();
 
   LWIP_ERROR("netif != NULL", (netif != NULL), return;);

Drivers/LwIP/src/core/ipv4/icmp.c

@@ -87,7 +87,6 @@ icmp_input(struct pbuf *p, struct netif *inp)
   const struct ip_hdr *iphdr_in;
   u16_t hlen;
   const ip4_addr_t *src;
-
   ICMP_STATS_INC(icmp.recv);
   MIB2_STATS_INC(mib2.icmpinmsgs);
 

Drivers/LwIP/src/netif/ethernetif.c

@@ -47,7 +47,7 @@ void ethernetif_set_irq_pending(void)
 
 uint8_t ethernetif_is_irq_pending(void)
 {
-    return 0u;
+    return ch390_runtime_is_irq_pending();
 }
 
 static void low_level_init(struct netif *netif)
@@ -62,8 +62,7 @@ static err_t low_level_output(struct netif *netif, struct pbuf *p)
 
 static struct pbuf *low_level_input(struct netif *netif)
 {
-    LWIP_UNUSED_ARG(netif);
-    return NULL;
+    return ch390_runtime_input_frame(netif);
 }
 
 void ethernetif_input(struct netif *netif)