selftests/net/forwarding: add Makefile to install tests

Add missing Makefile for net/forwarding tests and include it to
the targets list, otherwise forwarding tests are not installed
in case of cross-compilation.

Signed-off-by: Vadym Kochan <vadym.kochan@plvision.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 6ec5039..b93fa64 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -33,6 +33,7 @@
 TARGETS += mount
 TARGETS += mqueue
 TARGETS += net
+TARGETS += net/forwarding
 TARGETS += net/mptcp
 TARGETS += netfilter
 TARGETS += networking/timestamping