Description of problem:
The FRR reloader causes eBGP connection flapping when eBGP multihop peer with default TTL (255) is unchanged.

When creating an eBGP multihop without TTL, FRR will default the TTL to 255 and show it in a vtysh 'running-configuration' command which is used by the frr-reload script to calculate new configuration deltas.

Version-Release number of selected component (if applicable):
7.5.1

How reproducible:
100%

Steps to Reproduce:
1. Create /etc/frr/frr.conf
frr version 7.5
frr defaults traditional
hostname centos8.localdomain
no ip forwarding
no ipv6 forwarding
service integrated-vtysh-config
line vty
router bgp 4250001000
neighbor 192.168.122.207 remote-as 65512
neighbor 192.168.122.207 ebgp-multihop

2. Start FRR

1. systemctl start frr

3. Show running configuration. Note that FRR explicitly set and shows the default TTL (225)

1. vtysh -c 'show running-config'
   Building configuration...

Current configuration:
!
frr version 7.5
frr defaults traditional
hostname centos8.localdomain
no ip forwarding
no ipv6 forwarding
service integrated-vtysh-config
!
router bgp 4250001000
neighbor 192.168.122.207 remote-as 65512
neighbor 192.168.122.207 ebgp-multihop 255
!
line vty
!
end

4. Copy initial frr.conf to frr.conf.new (no changes)

1. cp /etc/frr/frr.conf /root/frr.conf.new

5. Run frr-reload.sh:

1. /usr/lib/frr/frr-reload.py --test /root/frr.conf.new
   2023-08-20 20:15:48,050 INFO: Called via "Namespace(bindir='/usr/bin', confdir='/etc/frr', daemon='', debug=False, filename='/root/frr.conf.new', input=None, log_level='info', overwrite=False, pathspace=None, reload=False, rundir='/var/run/frr', stdout=False, test=True, vty_socket=None)"
   2023-08-20 20:15:48,050 INFO: Loading Config object from file /root/frr.conf.new
   2023-08-20 20:15:48,124 INFO: Loading Config object from vtysh show running

Lines To Delete
===============
router bgp 4250001000
no neighbor 192.168.122.207 ebgp-multihop 255

Lines To Add
============
router bgp 4250001000
neighbor 192.168.122.207 ebgp-multihop

As seen above, the FRR reloader wants to remove the BGP peer and re-add it. This causes the reported BGP peering flapping issue.

I also reproduced this issue on the latest stable upstream FRR frr-9.0-01.el9.x86_64.