staging: vt6656: removed unused IS_NULL_ADDRESS definition

Removed custom definition not used elsewhere, is_zero_ether_addr()
is already provided if required.
Signed-off-by: Andres More <more.andres@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/vt6656/tether.h

@@ -197,12 +197,6 @@ typedef struct tagS802_11Header {
 S802_11Header, *PS802_11Header;
 
 /*---------------------  Export Macros ------------------------------*/
-// Frame type macro
-
-#define IS_NULL_ADDRESS(pbyEtherAddr) (             \
-    (*(PDWORD)(pbyEtherAddr) == 0L) &&              \
-    (*(PWORD)((PBYTE)(pbyEtherAddr) + 4) == 0)      \
-)
 
 /*---------------------  Export Classes  ----------------------------*/