selftests: forwarding: lib: Support NUM_NETIFS of 0

So far the case of NUM_NETIFS of 0 has not been interesting. However if
one wishes to reuse the lib.sh routines in a setup of a separate
namespace, being able to import like this is handy.

Therefore replace the {1..$NUM_NETIFS} references, which cause iteration
over 1 and 0, with an explicit for loop like we do in setup_wait() and
tc_offload_check(), so that for NUM_NETIFS of 0 no iteration is done.
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -104,7 +104,7 @@ create_netif_veth()
 {
 	local i
 
-	for i in $(eval echo {1..$NUM_NETIFS}); do
+	for ((i = 1; i <= NUM_NETIFS; ++i)); do
 		local j=$((i+1))
 
 		ip link show dev ${NETIFS[p$i]} &> /dev/null
@@ -135,7 +135,7 @@ if [[ "$NETIF_CREATE" = "yes" ]]; then
 	create_netif
 fi
 
-for i in $(eval echo {1..$NUM_NETIFS}); do
+for ((i = 1; i <= NUM_NETIFS; ++i)); do
 	ip link show dev ${NETIFS[p$i]} &> /dev/null
 	if [[ $? -ne 0 ]]; then
 		echo "SKIP: could not find all required interfaces"