selftests: lib: tc_rule_stats_get(): Move default to argument definition

The argument $dir has a fallback value of "ingress". Move the fallback from
the usage site to the argument definition block to make the fact clearer.
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/lib.sh

@@ -199,10 +199,10 @@ tc_rule_stats_get()
 {
 	local dev=$1; shift
 	local pref=$1; shift
-	local dir=$1; shift
+	local dir=${1:-ingress}; shift
 	local selector=${1:-.packets}; shift
 
-	tc -j -s filter show dev $dev ${dir:-ingress} pref $pref \
+	tc -j -s filter show dev $dev $dir pref $pref \
 	    | jq ".[1].options.actions[].stats$selector"
 }