fengzi: Fix LM3S ETH driver: Ethernet RX interrupt will be disabled if pbuf_alloc failed.

bsp/lm3s8962/drivers/luminaryif.c

@@ -424,6 +424,10 @@ struct pbuf * luminaryif_rx(rt_device_t dev)
         lwip_stats.link.memerr++;
         lwip_stats.link.drop++;
 #endif
+        // 
+        // Enable Ethernet RX Interrupt. 
+        // 
+        EthernetIntEnable(ETH_BASE, ETH_INT_RX); 
     }
 	
     return(p);

bsp/lm3s9b9x/drivers/luminaryif.c

@@ -423,6 +423,10 @@ struct pbuf * luminaryif_rx(rt_device_t dev)
         lwip_stats.link.memerr++;
         lwip_stats.link.drop++;
 #endif
+        // 
+        // Enable Ethernet RX Interrupt. 
+        // 
+        EthernetIntEnable(ETH_BASE, ETH_INT_RX); 
     }
 
     return(p);