[PATCH] e1000: Fix PBA allocation calculations

Assign the PBA to be large enough to contain at least 2 jumbo frames on
all adapters. This dramatically increases performance on several adapters
and fixes TX performance degradation issues where the PBA was misallocated
in the old algorithm.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/net/e1000/e1000_hw.h

@@ -2422,6 +2422,7 @@ struct e1000_host_command_info {
 #define E1000_PBA_8K 0x0008    /* 8KB, default Rx allocation */
 #define E1000_PBA_12K 0x000C    /* 12KB, default Rx allocation */
 #define E1000_PBA_16K 0x0010    /* 16KB, default TX allocation */
+#define E1000_PBA_20K 0x0014
 #define E1000_PBA_22K 0x0016
 #define E1000_PBA_24K 0x0018
 #define E1000_PBA_30K 0x001E