settings: preserve existing connection flags on update
We are passing to the plugin only 'sett_flags', which is the bitmask of flags to change and works together with 'sett_mask'; however, plugins interpret that value as the new flags value. The result is that if there is no change needed (0/0), the existing flags are lost. Simple reproducer:
ip link add dummy1 type dummy
ip link set dummy1 up
ip addr add dev dummy1 fd01::12/64
sleep 1
# now, a external connection is created by NM
echo "BEFORE:"
cat /run/NetworkManager/system-connections/dummy1.nmconnection | grep "nm-generated\|volatile\|external"
# just add a new address to the interface to make it lose
# the external flag
ip addr add dev dummy1 172.25.42.1/24
sleep 1
echo "AFTER:"
cat /run/NetworkManager/system-connections/dummy1.nmconnection | grep "nm-generated\|volatile\|external"
Output:
BEFORE:
nm-generated=true
volatile=true
external=true
AFTER:
Fixes: d35d3c46 ('settings: rework tracking settings connections and settings plugins')