udhcp: pass pointer to whole packet to "add option" functions

This is needed for "overflow option" support

function                                             old     new   delta
udhcp_find_option                                      -      34     +34
udhcp_add_binary_option                               94     106     +12
write_leases                                         227     223      -4
udhcp_init_header                                     86      82      -4
send_release                                         104      99      -5
init_packet                                           87      81      -6
add_client_options                                   160     154      -6
add_server_options                                   100      92      -8
udhcpd_main                                         1964    1954     -10
udhcpc_main                                         2859    2837     -22
find_option                                           34       -     -34
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 1/8 up/down: 46/-99)            Total: -53 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/udhcp/files.c b/networking/udhcp/files.c
index 1f25bb1..cf55a6b 100644
--- a/networking/udhcp/files.c
+++ b/networking/udhcp/files.c
@@ -167,10 +167,11 @@
 	close(fd);
 
 	if (server_config.notify_file) {
-// TODO: vfork-based child creation
-		char *cmd = xasprintf("%s %s", server_config.notify_file, server_config.lease_file);
-		system(cmd);
-		free(cmd);
+		char *argv[3];
+		argv[0] = server_config.notify_file;
+		argv[1] = server_config.lease_file;
+		argv[2] = NULL;
+		spawn_and_wait(argv);
 	}
 }