mcast-tools: fix linux/pim.h include

fix wrong struct in pim.h big endian case
it leads to compile error on ar71xx and other arch
Error was:
In file included from debug.c:71:0:
../include/linux/pim.h:14:3: error: expected specifier-qualifier-list before 'pim_type'
   pim_type:4;  /* PIM message type */
   ^
make[6]: *** [debug.o] Error 1

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>