Fix SIGHUP: reload config instead of shutting down

SIGHUP was treated identically to SIGTERM, causing the filter to exit.
Unix convention is that SIGHUP triggers a configuration reload in
long-running daemons. The reload path already exists (previously only
reachable via SIGUSR1); SIGHUP is now folded into it.

SIGUSR1 continues to work as before. SIGTERM and SIGINT remain the
shutdown signals.

Fixes: trusteddomainproject#322

Author: thegushi

opendmarc/opendmarc.8.in

@@ -128,7 +128,11 @@ output.
 Print the version number, whether SPF support is compiled in, and the
 libmilter version, and then exit without doing anything else.
 .SH SIGNALS
-Upon receiving SIGUSR1, if the filter was started with a configuration
+Upon receiving
+.B SIGHUP
+or
+.BR SIGUSR1 ,
+if the filter was started with a configuration
 file, it will be re-read and the new values used.  Note that any
 command line overrides provided at startup time will be lost when this is
 done.  Also, the following configuration file values (and their corresponding

opendmarc/opendmarc.c

@@ -3849,12 +3849,12 @@ struct smfiDesc smfilter =
 static void
 dmarcf_sighandler(int sig)
 {
-	if (sig == SIGINT || sig == SIGTERM || sig == SIGHUP)
+	if (sig == SIGINT || sig == SIGTERM)
 	{
 		diesig = sig;
 		die = TRUE;
 	}
-	else if (sig == SIGUSR1)
+	else if (sig == SIGHUP || sig == SIGUSR1)
 	{
 		if (conffile != NULL)
 			reload = TRUE;