tests: add ifquery test for gre dependency learning

tests/fixtures/gre.interfaces

@@ -0,0 +1,12 @@
+auto tun0
+iface tun0
+	gre-local 203.0.113.2
+	gre-remote 203.0.113.1
+	gre-dev eth0
+	gre-ttl 255
+	gre-flags nopmtudisc ignore-df
+	address 203.0.113.10/30
+	gateway 203.0.113.9
+
+iface eth0
+	address 203.0.113.2/30

tests/ifquery_test

@@ -28,7 +28,8 @@ tests_init \
 	tunnel_legacy_dependency \
 	tunnel_legacy_rewrite \
 	tunnel_ifupdown2_dependency \
-	tunnel_ifupdown2_rewrite
+	tunnel_ifupdown2_rewrite \
+	gre_dependency
 
 noargs_body() {
 	atf_check -s exit:1 -e ignore ifquery -S/dev/null
@@ -180,3 +181,8 @@ tunnel_ifupdown2_rewrite_body() {
 		-o match:"tunnel-ttl 255" \
 		ifquery -E $EXECUTORS_LINUX -i $FIXTURES/tunnel-ifupdown2.interfaces tun0
 }
+
+gre_dependency_body() {
+	atf_check -s exit:0 -o match:"requires eth0" \
+		ifquery -E $EXECUTORS_LINUX -i $FIXTURES/gre.interfaces tun0
+}