selftests: forwarding: Add MAC get helper

Signed-off-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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

@@ -270,6 +270,13 @@ link_stats_tx_packets_get()
        ip -j -s link show dev $if_name | jq '.[]["stats64"]["tx"]["packets"]'
 }
 
+mac_get()
+{
+	local if_name=$1
+
+	ip -j link show dev $if_name | jq -r '.[]["address"]'
+}
+
 bridge_ageing_time_get()
 {
 	local bridge=$1