init: use init's property expansion code for setprop/write

Change-Id: I3c284860cc8d5106ac2b086e62baeb6263873935
Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/init/init_parser.h b/init/init_parser.h
index ff13b04..b078cad 100644
--- a/init/init_parser.h
+++ b/init/init_parser.h
@@ -31,5 +31,6 @@
 void queue_builtin_action(int (*func)(int nargs, char **args), char *name);
 
 int init_parse_config_file(const char *fn);
+int expand_props(char *dst, const char *src, int len);
 
 #endif