GRE: add encapsulation gre and gretap

[sever-sever]

Change Summary

GRE: Add tunnel-type erspan, l3 and teb

Add tunnel type
 - erspan
 - l3
 - teb (Transparent Ethernet Bridge)

By default L3 GRE interfaces cannot be bridged to a bridge interface.
Add the ability to change tunnel type.

set vpp interfaces gre gre2 tunnel-type 'teb

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)
• Other (please describe):

Related Task(s)

Related PR(s)

Proposed changes

How to test

Add two GRE tunnels, with gre and gretap encapsulation

set vpp settings interface eth1 driver 'dpdk'

set vpp interfaces gre gre2 remote '192.0.2.2'
set vpp interfaces gre gre2 source-address '192.0.2.1'
set vpp interfaces gre gre2 tunnel-type 'teb'
set vpp interfaces gre gre3 remote '203.0.113.3'
set vpp interfaces gre gre3 source-address '192.0.2.1'
set vpp interfaces gre gre4 remote '192.0.2.42'
set vpp interfaces gre gre4 source-address '192.0.2.1'
set vpp interfaces gre gre4 tunnel-type 'erspan'

set vpp interfaces bridge br1 member interface 'eth1'
set vpp interfaces bridge br1 member interface 'gre2'

set vpp settings logging default-log-level 'debug'
set vpp settings unix poll-sleep-usec '10'

Instance 2 (l2), instance 3 (l3)

vyos@r14# sudo vppctl show gre tunnel
[0] instance 2 src 192.0.2.1 dst 192.0.2.2 fib-idx 0 sw-if-idx 3 payload TEB point-to-point l2-adj-idx 3 
[1] instance 3 src 192.0.2.1 dst 203.0.113.3 fib-idx 0 sw-if-idx 4 payload L3 point-to-point 
[2] instance 4 src 192.0.2.1 dst 192.0.2.42 fib-idx 0 sw-if-idx 5 payload ERSPAN point-to-point session 0 l2-adj-idx 4 
[edit]
vyos@r14# 

Check bridge-domain:

vyos@r14# sudo vppctl show bridge-domain 1 detail
  BD-ID   Index   BSN  Age(min)  Learning  U-Forwrd   UU-Flood   Flooding  ARP-Term  arp-ufwd Learn-co Learn-li   BVI-Intf 
    1       1      0     off        on        on       flood        on       off       off        1    16777216     N/A    
span-l2-input l2-input-classify l2-input-feat-arc l2-policer-classify l2-input-acl vpath-input-l2 l2-ip-qos-record l2-input-vtr l2-learn l2-rw l2-fwd l2-flood l2-flood l2-output 

           Interface           If-idx ISN  SHG  BVI  TxFlood        VLAN-Tag-Rewrite       
             eth1                1     1    0    -      *                 none             
             gre2                4     1    0    -      *                 none             
[edit]
vyos@r14# 

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