selftests: net: lib: Add a couple autodefer helpers

JIRA: https://issues.redhat.com/browse/RHEL-96617

commit 976d248
Author: Petr Machata <petrm@nvidia.com>
Date:   Wed Dec 18 18:15:58 2024 +0100

    selftests: net: lib: Add a couple autodefer helpers

    Alongside the helper ip_link_set_up(), one to set the link down will be
    useful as well. Add a helper to determine the link state as well,
    ip_link_is_up(), and use it to short-circuit any changes if the state is
    already the desired one.

    Furthermore, add a helper bridge_vlan_add().

    Signed-off-by: Petr Machata <petrm@nvidia.com>
    Reviewed-by: Ido Schimmel <idosch@nvidia.com>
    Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
    Link: https://patch.msgid.link/856d9e01725fdba21b7f6716358f645b19131af2.1734540770.git.petrm@nvidia.com
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: CKI Backport Bot <cki-ci-bot+cki-gitlab-backport-bot@redhat.com>

Author: CKI Backport Bot

tools/testing/selftests/net/lib.sh

@@ -477,12 +477,33 @@ ip_link_set_addr()
 	defer ip link set dev "$name" address "$old_addr"
 }
 
+ip_link_is_up()
+{
+	local name=$1; shift
+
+	local state=$(ip -j link show "$name" |
+		      jq -r '(.[].flags[] | select(. == "UP")) // "DOWN"')
+	[[ $state == "UP" ]]
+}
+
 ip_link_set_up()
 {
 	local name=$1; shift
 
-	ip link set dev "$name" up
-	defer ip link set dev "$name" down
+	if ! ip_link_is_up "$name"; then
+		ip link set dev "$name" up
+		defer ip link set dev "$name" down
+	fi
+}
+
+ip_link_set_down()
+{
+	local name=$1; shift
+
+	if ip_link_is_up "$name"; then
+		ip link set dev "$name" down
+		defer ip link set dev "$name" up
+	fi
 }
 
 ip_addr_add()
@@ -498,3 +519,9 @@ ip_route_add()
 	ip route add "$@"
 	defer ip route del "$@"
 }
+
+bridge_vlan_add()
+{
+	bridge vlan add "$@"
+	defer bridge vlan del "$@"
+}