ixgb: eliminate checkstack warnings

Really trivial fix, use kmalloc/kfree instead of stack space.
use static const instead of const to further reduce stack usage.

V2: reflect changes suggested by Joe Perches

before:
[jbrandeb@jbrandeb-mobl2 linux-2.6]$ make checkstack|grep '\[ixgb\]'
0x00000fc1 ixgb_set_multi [ixgb]:                       768
0x00001031 ixgb_set_multi [ixgb]:                       768
0x000010f2 ixgb_set_multi [ixgb]:                       768
0x061c ixgb_check_options [ixgb]:                       448
0x09c3 ixgb_check_options [ixgb]:                       448
0x0000649e ixgb_set_ringparam [ixgb]:                   192
0x0000130d ixgb_xmit_frame [ixgb]:                      184
0x000019e0 ixgb_xmit_frame [ixgb]:                      184
0x00002267 ixgb_clean [ixgb]:                           152
0x00002673 ixgb_clean [ixgb]:                           152

after:
0x000064ee ixgb_set_ringparam [ixgb]:                   192
0x0000135d ixgb_xmit_frame [ixgb]:                      184
0x00001a30 ixgb_xmit_frame [ixgb]:                      184
0x000022b7 ixgb_clean [ixgb]:                           152
0x000026c3 ixgb_clean [ixgb]:                           152

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/intel/ixgb/ixgb_hw.h b/drivers/net/ethernet/intel/ixgb/ixgb_hw.h
index 873d32b..2a99a35 100644
--- a/drivers/net/ethernet/intel/ixgb/ixgb_hw.h
+++ b/drivers/net/ethernet/intel/ixgb/ixgb_hw.h
@@ -97,8 +97,6 @@
 	ixgb_bus_width_64
 } ixgb_bus_width;
 
-#define IXGB_ETH_LENGTH_OF_ADDRESS   6
-
 #define IXGB_EEPROM_SIZE    64	/* Size in words */
 
 #define SPEED_10000  10000
@@ -674,7 +672,7 @@
 	u32 max_frame_size;	/* Maximum frame size supported     */
 	u32 mc_filter_type;	/* Multicast filter hash type       */
 	u32 num_mc_addrs;	/* Number of current Multicast addrs */
-	u8 curr_mac_addr[IXGB_ETH_LENGTH_OF_ADDRESS];	/* Individual address currently programmed in MAC */
+	u8 curr_mac_addr[ETH_ALEN];	/* Individual address currently programmed in MAC */
 	u32 num_tx_desc;	/* Number of Transmit descriptors   */
 	u32 num_rx_desc;	/* Number of Receive descriptors    */
 	u32 rx_buffer_size;	/* Size of Receive buffer           */