ENCx24J600 UDP backlog support from Maz Holtzberg

ChangeLog

@@ -5621,4 +5621,6 @@
 	  From Rashid Fatah (2013-9-23).
 	* arch/arm/src/sama5/sam_hsmci.c:  TX DMA disabled.  It is just not
 	  reliable. No idea why.  RX DMA is still used (2013-9-23).
+	* driver/net/encx24j600.c:  UDP/RXAVAIL backlog support from Max
+	  Holtzberg (2013-9-24).
 

drivers/net/Kconfig

@@ -93,6 +93,7 @@ config ENCX24J600
 	bool "Microchip ENCX24J600 support"
 	default n
 	select SPI
+	select NET_RXAVAIL
 	---help---
 		References:
 		ENC424J600/624J600 Data Sheet Stand-Alone 10/100 Ethernet Controller
@@ -123,6 +124,15 @@ config ENCX24J600_FREQUENCY
 	---help---
 		Define to use a different bus frequency
 
+config ENCX24J600_NDESCR
+	int "Descriptor Count"
+	default 16
+	---help---
+		Defines how many descriptors are preallocated for the
+		transmission and reception queues.
+		The ENC has a relative large packet buffer of 24kB which can
+		be used to buffer multiple packets silmutaneously
+
 config ENCX24J600_STATS
 	bool "Network statistics support"
 	default n