selftests: net: lib.sh: Don't defer failed commands

Usually the autodefer helpers in lib.sh are expected to be run in context
where success is the expected outcome. However when using them for feature
detection, failure can legitimately occur. But the failed command still
schedules a cleanup, which will likely fail again.

Instead, only schedule deferred cleanup when the positive command succeeds.

This way of organizing the cleanup has the added benefit that now the
return code from these functions reflects whether the command passed.

Signed-off-by: Petr Machata <[email protected]>
Acked-by: Nikolay Aleksandrov <[email protected]>
Link: https://patch.msgid.link/af10a5bb82ea11ead978cf903550089e006d7e70.1757004393.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <[email protected]>

Author: pmachata

tools/testing/selftests/net/lib.sh

@@ -547,17 +547,17 @@ ip_link_add()
 {
 	local name=$1; shift
 
-	ip link add name "$name" "$@"
-	defer ip link del dev "$name"
+	ip link add name "$name" "$@" && \
+		defer ip link del dev "$name"
 }
 
 ip_link_set_master()
 {
 	local member=$1; shift
 	local master=$1; shift
 
-	ip link set dev "$member" master "$master"
-	defer ip link set dev "$member" nomaster
+	ip link set dev "$member" master "$master" && \
+		defer ip link set dev "$member" nomaster
 }
 
 ip_link_set_addr()
@@ -566,8 +566,8 @@ ip_link_set_addr()
 	local addr=$1; shift
 
 	local old_addr=$(mac_get "$name")
-	ip link set dev "$name" address "$addr"
-	defer ip link set dev "$name" address "$old_addr"
+	ip link set dev "$name" address "$addr" && \
+		defer ip link set dev "$name" address "$old_addr"
 }
 
 ip_link_has_flag()
@@ -590,8 +590,8 @@ ip_link_set_up()
 	local name=$1; shift
 
 	if ! ip_link_is_up "$name"; then
-		ip link set dev "$name" up
-		defer ip link set dev "$name" down
+		ip link set dev "$name" up && \
+			defer ip link set dev "$name" down
 	fi
 }
 
@@ -600,29 +600,29 @@ 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 "$name" up
+		ip link set dev "$name" down && \
+			defer ip link set dev "$name" up
 	fi
 }
 
 ip_addr_add()
 {
 	local name=$1; shift
 
-	ip addr add dev "$name" "$@"
-	defer ip addr del dev "$name" "$@"
+	ip addr add dev "$name" "$@" && \
+		defer ip addr del dev "$name" "$@"
 }
 
 ip_route_add()
 {
-	ip route add "$@"
-	defer ip route del "$@"
+	ip route add "$@" && \
+		defer ip route del "$@"
 }
 
 bridge_vlan_add()
 {
-	bridge vlan add "$@"
-	defer bridge vlan del "$@"
+	bridge vlan add "$@" && \
+		defer bridge vlan del "$@"
 }
 
 wait_local_port_listen()