selftests: forwarding: fix learning_test when h1 supports IFF_UNICAST_FLT

The first host interface has by default no interest in receiving packets
MAC DA de:ad:be:ef:13:37, so it might drop them before they hit the tc
filter and this might confuse the selftest.

Enable promiscuous mode such that the filter properly counts received
packets.

Fixes: d4deb01467 ("selftests: forwarding: Add a test for FDB learning")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

tools/testing/selftests/net/forwarding/lib.sh

@@ -1240,6 +1240,7 @@ learning_test()
 	# FDB entry was installed.
 	bridge link set dev $br_port1 flood off
 
+	ip link set $host1_if promisc on
 	tc qdisc add dev $host1_if ingress
 	tc filter add dev $host1_if ingress protocol ip pref 1 handle 101 \
 		flower dst_mac $mac action drop
@@ -1289,6 +1290,7 @@ learning_test()
 
 	tc filter del dev $host1_if ingress protocol ip pref 1 handle 101 flower
 	tc qdisc del dev $host1_if ingress
+	ip link set $host1_if promisc off
 
 	bridge link set dev $br_port1 flood on