bgp: T3225: is_addr_assigned should check only ipv4 ipv6 neighbors

[sever-sever]

Change Summary

is_addr_assigned should check only ipv4 and ipv6 neighbors and don't check "interface neighbors"

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

T3225

Component(s) name

bgp

Proposed changes

How to test

set interfaces ethernet eth1 address 192.0.2.1/24
set protocols bgp 64501 neighbor eth1 interface remote-as '64501'
set protocols bgp 64501 neighbor 192.0.2.1 remote-as 65002

vyos@r-roll01# commit
[ protocols bgp 64501 ]
Can't configure local address as neighbor "192.0.2.1"

[[protocols bgp 64501]] failed
Commit failed

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly