selftests/bpf: install files test_xdp_vlan.sh

When ./test_xdp_vlan_mode_generic.sh runs it complains that it can't
find file test_xdp_vlan.sh.

 # selftests: bpf: test_xdp_vlan_mode_generic.sh
 # ./test_xdp_vlan_mode_generic.sh: line 9: ./test_xdp_vlan.sh: No such
 file or directory

Rework so that test_xdp_vlan.sh gets installed, added to the variable
TEST_PROGS_EXTENDED.

Fixes: d35661fc ("selftests/bpf: add wrapper scripts for test_xdp_vlan.sh")
Signed-off-by: NAnders Roxell <anders.roxell@linaro.org>
Acked-by: NJesper Dangaard Brouer <jbrouer@redhat.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/Makefile

@@ -71,7 +71,8 @@ TEST_PROGS := test_kmod.sh \
 TEST_PROGS_EXTENDED := with_addr.sh \
 	with_tunnels.sh \
 	tcp_client.py \
-	tcp_server.py
+	tcp_server.py \
+	test_xdp_vlan.sh
 
 # Compile but not part of 'make run_tests'
 TEST_GEN_PROGS_EXTENDED = test_libbpf_open test_sock_addr test_skb_cgroup_id_user \