Add FQDN capability

It's not kinda RFC (draft), but it's implemented and used in various
other open-source software like FRRouting, Bird, ExaBGP.

It's very handy when dealing with lots of peers.

Exampe between GoBGP and FRRouting:
```
% ./cmd/gobgp/gobgp neighbor 192.168.10.123 | grep -A4 fqdn:
    fqdn:       advertised and received
      Local:
         name: donatas-pc, domain:
      Remote:
         name: exit1-debian-9, domain:
```

```
% vtysh -c 'show bgp neighbors 192.168.10.17 json' | jq .'"192.168.10.17".neighborCapabilities.hostName'
{
  "advHostName": "exit1-debian-9",
  "advDomainName": "n/a",
  "rcvHostName": "donatas-pc",
  "rcvDomainName": "n/a"
}
```

Signed-off-by: Donatas Abraitis <donatas.abraitis@gmail.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/internal/pkg/apiutil/capability.go b/internal/pkg/apiutil/capability.go
index d135713a..125427db 100644
--- a/internal/pkg/apiutil/capability.go
+++ b/internal/pkg/apiutil/capability.go
@@ -110,6 +110,15 @@ func NewRouteRefreshCiscoCapability(a *bgp.CapRouteRefreshCisco) *api.RouteRefre
 	return &api.RouteRefreshCiscoCapability{}
 }
 
+func NewFQDNCapability(a *bgp.CapFQDN) *api.FQDNCapability {
+	return &api.FQDNCapability{
+		HostNameLen:   uint32(a.HostNameLen),
+		HostName:      a.HostName,
+		DomainNameLen: uint32(a.DomainNameLen),
+		DomainName:    a.DomainName,
+	}
+}
+
 func NewUnknownCapability(a *bgp.CapUnknown) *api.UnknownCapability {
 	return &api.UnknownCapability{
 		Code:  uint32(a.CapCode),
@@ -140,6 +149,8 @@ func MarshalCapability(value bgp.ParameterCapabilityInterface) (*any.Any, error)
 		m = NewLongLivedGracefulRestartCapability(n)
 	case *bgp.CapRouteRefreshCisco:
 		m = NewRouteRefreshCiscoCapability(n)
+	case *bgp.CapFQDN:
+		m = NewFQDNCapability(n)
 	case *bgp.CapUnknown:
 		m = NewUnknownCapability(n)
 	default:
@@ -227,6 +238,8 @@ func unmarshalCapability(a *any.Any) (bgp.ParameterCapabilityInterface, error) {
 		return bgp.NewCapLongLivedGracefulRestart(tuples), nil
 	case *api.RouteRefreshCiscoCapability:
 		return bgp.NewCapRouteRefreshCisco(), nil
+	case *api.FQDNCapability:
+		return bgp.NewCapFQDN(a.HostName, a.DomainName), nil
 	case *api.UnknownCapability:
 		return bgp.NewCapUnknown(bgp.BGPCapabilityCode(a.Code), a.Value), nil
 	}