core: allow interface altnames in RestrictNetworkInterfaces=

This patch enables IFNAME_VALID_ALTERNATIVE for checks guarding the
parsing of RestrictNetworkInterfaces=.

The underlying implementation for this option already supports
altnames.

test/units/testsuite-62-6.service

@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Unit]
+Description=TEST-62-RESTRICT-IFACES-altname
+[Service]
+ExecStart=/bin/sh -c 'ping -c 1 -W 0.2 192.168.113.1'
+ExecStart=/bin/sh -c 'ping -c 1 -W 0.2 192.168.113.5'
+ExecStart=/bin/sh -c '! ping -c 1 -W 0.2 192.168.113.9'
+RestrictNetworkInterfaces=veth0-altname-with-more-than-15-chars
+RestrictNetworkInterfaces=veth1-altname-with-more-than-15-chars
+Type=oneshot

test/units/testsuite-62.sh

@@ -17,6 +17,7 @@ setup() {
         ip -n "ns${i}" link set dev lo up
         ip -n "ns${i}" addr add "192.168.113."$((4*i+1))/30 dev "veth${i}_"
         ip link set dev "veth${i}" up
+        ip link property add dev "veth${i}" altname "veth${i}-altname-with-more-than-15-chars"
         ip addr add "192.168.113."$((4*i+2))/30 dev "veth${i}"
     done
 }