https://github.com/jpr5/ngrep/pull/28

From 52515bae377f221b5473d9040f5f43ab1c672672 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Mon, 19 Dec 2022 11:49:06 +0100
Subject: [PATCH] Include <err.h> and "tcpkill.h" to avoid implicit function
 declarations

Implicit function declarations are a historic language feature that
were removed from C in 1999.
--- a/ngrep.c
+++ b/ngrep.c
@@ -98,6 +98,7 @@
 #endif
 
 #include "ngrep.h"
+#include "tcpkill.h"
 
 
 /*
--- a/tcpkill.c
+++ b/tcpkill.c
@@ -14,6 +14,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
+#include <err.h>
 #include <libnet.h>
 #include <pcap.h>