VPP: T1797: Added interfaces reinitialization

[zdc]

Change Summary

Added interfaces reinitialization for VPP

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)

• https://vyos.dev/T1797

Component(s) name

VPP

Proposed changes

After an interface is added/removed from VPP, it will be reinitialized, which allows reconfiguring IP addresses on it.

Also modified VPP load priority to start before interfaces, and avoid reconfiguration during boot.

How to test

Add/delete interfaces to VPP. During this process they are destroyed and created again in the system, therefore config is always empty. With this change, they will be reinitialized according to CLI configuration:

set interfaces ethernet eth0 address '192.0.2.1/24'
set vpp interface eth0
commit

set interfaces ethernet eth0 address '192.0.2.1/24'
delete vpp interface eth0
commit

vyos@vyos# run show interfaces 
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface        IP Address                        S/L  Description
---------        ----------                        ---  -----------
eth0             192.0.2.1/24                      u/u  
lo               127.0.0.1/8                       u/u  
                 ::1/128                                

Checklist:

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