common: Avoid conflict with __bitwise macro from linux/types.h

common: Avoid conflict with __bitwise macro from linux/types.h

Undefine the __bitwise macro before defining it to avoid conflicts
with the one from linux/types.h; the same is done some lines above
when __CHECKER__ is defined. Fixes the following warning:

  In file included from ../src/l2_packet/l2_packet_linux.c:15:0:
  hostap/src/utils/common.h:438:0: warning: "__bitwise" redefined
   #define __bitwise

  In file included from /usr/include/linux/filter.h:9:0,
                   from ../src/l2_packet/l2_packet_linux.c:13:
  /usr/include/linux/types.h:21:0: note: this is the location of the previous definition
   #define __bitwise __bitwise__

Signed-off-by: Beniamino Galvani <bgalvani@redhat.com>