testminiwget.sh: use either "ip addr" or "ifconfig -a"

miniupnpc/testminiwget.sh

@@ -2,7 +2,7 @@
 # $Id: testminiwget.sh,v 1.15 2017/11/02 17:36:26 nanard Exp $
 # vim: tabstop=4 shiftwidth=4 noexpandtab
 # project miniupnp : http://miniupnp.free.fr/
-# (c) 2011-2018 Thomas Bernard
+# (c) 2011-2019 Thomas Bernard
 #
 # test program for miniwget.c
 # is usually invoked by "make check"
@@ -23,6 +23,12 @@ DOWNLOADEDFILE="${TMPD}/downloadedfile"
 PORT=
 RET=0
 IPCONFIG=$(which ifconfig)
+IP=$(which ip)
+if [ "$IP" ] ; then
+	if ! $IP addr | grep inet6 ; then
+		HAVE_IPV6=no
+	fi
+else
 	if [ -z "$IPCONFIG" ] ; then
 		IPCONFIG="/sbin/ifconfig"
 	fi
@@ -30,6 +36,7 @@ fi
 	if ! $IPCONFIG -a | grep inet6 ; then
 		HAVE_IPV6=no
 	fi
+fi
 
 case "$HAVE_IPV6" in
     n|no|0)