Fix: SR-OS does not support unnumbered EBGP sessions (#2314)

One has to admire the incredible audacity of a developer who
sets 'features.bgp.ipv6_lla' flag to True while leaving a
"TODO BGP unnumbered" comment in the configuration template
(but hey, at least he left that comment)

Alas, faced with either implementing the missing functionality or
disabling the feature, I decided to take the easy way out.

A brave soul wanting to revert this decision is most welcome to
submit a working PR.

Author: ipspace

netsim/devices/sros.yml

@@ -32,7 +32,7 @@ features:
     vrf_local_as: True
     local_as_ibgp: True
     activate_af: True
-    ipv6_lla: True
+    ipv6_lla: False
   evpn:
     irb: True
     asymmetrical_irb: True