Rewrite function declarators without prototypes

This syntax is removed in C2x proposal N2841.

Test: presubmit
Change-Id: I3b067023327ed22dffda698c5f1accde60d95839
diff --git a/libnetutils/dhcpclient.c b/libnetutils/dhcpclient.c
index 11c116a..ad6898c 100644
--- a/libnetutils/dhcpclient.c
+++ b/libnetutils/dhcpclient.c
@@ -45,7 +45,7 @@
 
 typedef unsigned long long msecs_t;
 #if VERBOSE
-void dump_dhcp_msg();
+void dump_dhcp_msg(dhcp_msg *msg, int len);
 #endif
 
 msecs_t get_msecs(void)