Needed for the mISDN/mISDNif.h header structs, linux/types.h only
provides them for kernel code:

In file included from src/ftmod/ftmod_misdn/ftmod_misdn.c:51:
/usr/include/mISDN/mISDNif.h:296: error: expected specifier-qualifier-list before 'u_int'
/usr/include/mISDN/mISDNif.h:306: error: expected specifier-qualifier-list before 'u_int'
/usr/include/mISDN/mISDNif.h:339: error: expected ')' before 'nr'
...
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>