frr-reload: fix deleting active interface

[hedrok]

Make frr-reload use 'no interface' only for deleted interfaces, for active interfaces don't run 'no interface', run 'no' for all commands in interface section.

This was the behavior before #16723, which was a fix for case when interface was deleted from system: in this case inner commands with 'no' failed, and 'no interface' works.

But if interface is still active and whole configuration for the interface is deleted FRR issues error 'Failed to create cfgdata: only inactive interfaces can be deleted', so in this case it is proper to run 'no' version of all commands in section, but not 'no interface'.

How to test:

sudo ip link add dum771 type dummy
sudo ip link add dum881 type dummy

cat > frr-clean.conf << EOF
frr version 10.6-dev
frr defaults traditional
hostname r1
log syslog notifications
log timestamp precision 3
no log unique-id
service integrated-vtysh-config
!
EOF

cat > frr-with-interfaces.conf << EOF
frr version 10.6-dev
frr defaults traditional
hostname r1
log syslog notifications
log timestamp precision 3
no log unique-id
service integrated-vtysh-config
!
interface dum771
 ip address 10.77.0.1/24
exit
!
interface dum881
 ip address 10.88.0.1/24
exit
!
EOF
sudo /usr/lib/frr/frr-reload.py --reload frr-with-interfaces.conf

sudo ip link delete dum771

# Now `vtysh -c 'configure' -c 'no interface dum881'` results in error (current behaviour of frr-reload):

#% Configuration failed.
#
#commit failed session-id 1119 on Unknown-FD-16 req-id 3 source-ds: candidate target-ds: running validate-only: 0: reason: 'Failed to create cfgdata: only inactive interfaces can be deleted'

# I couldn't reproduce error in case of per-line 'no' deletion of parameters for dum881 (behaviour before PR #16723), but I didn't test GRE tunnels

# So after changes in this PR
sudo /usr/lib/frr/frr-reload.py --test frr-clean.conf

# gives:
# > Lines To Delete
# > ===============
# > no interface dum771
# > interface dum881
# >  no ip address 10.88.0.1/24
# > exit

# And can be applied cleanly:
sudo /usr/lib/frr/frr-reload.py --reload frr-clean.conf

[hedrok]

During meeting it was decided not to add dependencies on system state in frr-reload.py