[BGP]: Convert ip address to network address for the LOCAL_VLAN filter

[pavel-shirshov]

- Why I did it
To avoid log messages like:

Nov  5 22:12:10.741378 str-s6100-acs-1 INFO bgp#bgpd[55]: Prefix-list LOCAL_VLAN_IPV4_PREFIX prefix changed from 192.168.0.1/21 to 192.168.0.0/21 to match length
Nov  5 22:12:10.741378 str-s6100-acs-1 INFO bgp#bgpd[55]: Prefix-list LOCAL_VLAN_IPV6_PREFIX prefix changed from fc02:1000::1/64 to fc02:1000::/64 to match length

- How I did it
I used jinja2 filter inside of sonic-config-engine to convert ip host address with mask to the ip network address.

- How to verify it
Build an image and run on your DUT.
vtysh -c 'show run' | grep LOCAL_VLAN should show correct output

root@str-s6100-acs-1:~# sonic-cfggen -d -t /usr/share/sonic/templates/bgpd/bgpd.conf.j2 -y /etc/sonic/constants.yml | grep LOCAL_VLAN
ip prefix-list LOCAL_VLAN_IPV4_PREFIX seq 5 permit 192.168.0.0/21
ipv6 prefix-list LOCAL_VLAN_IPV6_PREFIX seq 10 permit fc02:1000::/64

- Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[pavel-shirshov]

retest broadcom please

[abdosi]

@pavel-shirshov Cherry-pick has conflict. Please create PR for 201911