radvd.c: make local function static
move set_interface_var to privsep-linux.c

...from device-linux.c, and make it a static function
send.c: make local functions static
radvdump.c: make local functions static
privsep-linux.c: make local functions static
gram.y: fix formatting of function definition
start check_conffile_permissions work
util.c: add strdupf

This function is for formatting strings without using fixed sized arrays
use strdupf