Duplicate IP addresses in the interface file are not handled well.

[VigneshSP94]

Issue

We happen to have a duplicate IP address in the interface file, when ifreload encounters duplicate IP, it stop processing and silently exits with status code 0.

info: vip: primary ip changed (from 100.0.7.30/32 to 100.0.5.234/32) we need to purge all ip addresses and re-add them #finds ip primary ip changes and deleteing all ips from the interface
info: vip: netlink: ip addr del 100.0.5.234/32 dev vip
info: vip: netlink: ip addr del 100.0.1.120/32 dev vip
..
..
info: vip: netlink: ip addr del 100.0.6.28/32 dev vip
info: vip: netlink: ip addr add 100.0.7.30/32 dev vip scope link #starts adding
info: vip: netlink: ip addr add 100.0.2.0/32 dev vip scope link 
info: vip: netlink: ip addr add 100.0.2.0/32 dev vip scope link # finds this ip second time
info: executing /etc/network/if-pre-up.d/wpasupplicant
info: executing /etc/network/if-up.d/wpasupplicant
info: executing /etc/network/if-up.d/postfix
info: executing /etc/network/if-up.d/nslcd
info: exit status 0 #quits silently with 

ifupdown2/ifupdown2/addons/address.py

Line 537 in 989508a

def __add_ip_addresses_with_attributes(self, ifaceobj, ifname, user_config_ip_addrs):

We added a print statement in this function to identify the error.

info: vip: netlink: ip addr add 100.0.4.0/32 dev vip scope link
info: vip: netlink: ip addr add 100.0.4.0/32 dev vip scope link
netlink: vip: cannot add address 100.0.4.0/32 dev vip: operation failed with 'File exists' (17) <====
info: executing /etc/network/if-pre-up.d/wpasupplicant
info: executing /etc/network/if-up.d/wpasupplicant
info: executing /etc/network/if-up.d/postfix
info: executing /etc/network/if-up.d/nslcd
info: exit status 0

ifreload version

#ifreload --version
ifupdown2:3.0.0-1

Expectation

ifreload should not exit with status code 0 during issue.
skipping duplicate addresses.