nic: Fix incorrect wrap handling of RX circular buffer

nic: move other nic functions into the dedicated nic files
uip: alloc buffer multiple of 8 bytes

Signed-off-by: João Silva <jgc3silva@gmail.com>

uip/uip-conf.h

@@ -132,6 +132,10 @@ typedef unsigned short uip_stats_t;
  */
 #define UIP_CONF_BUFFER_SIZE     1556
 
+/* Backing storage includes padding for the NIC's eight-byte DMA transfers.
+ * Keep UIP_CONF_BUFFER_SIZE as the logical frame/MSS limit. */
+#define UIP_CONF_BUFFER_ALLOC_SIZE ((UIP_CONF_BUFFER_SIZE + 7U) & ~7U)
+
 /**
  * Bytes of the buffer kept out of the advertised MSS.
  *