ixgbe: minor sparse fixes

Make strings const if possible, and fix includes so forward definitions
are seen.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/ixgbe/ixgbe.h b/drivers/net/ixgbe/ixgbe.h
index c160a7d..bc51432 100644
--- a/drivers/net/ixgbe/ixgbe.h
+++ b/drivers/net/ixgbe/ixgbe.h
@@ -244,7 +244,7 @@
 extern struct ixgbe_info ixgbe_82598AT_info;
 
 extern char ixgbe_driver_name[];
-extern char ixgbe_driver_version[];
+extern const char ixgbe_driver_version[];
 
 extern int ixgbe_up(struct ixgbe_adapter *adapter);
 extern void ixgbe_down(struct ixgbe_adapter *adapter);