bgpd: fix route-target display with as dotted format

bgpd: fix route-target display with as dotted format

The following command results in a wrong route-target
display:
> # show running-config
> [..]
> route-map rmap permit 1
>  set extcommunity rt 1.45:55
> exit
> router bgp 1.45 as-notation plain
> neighbor 192.0.2.1 remote-as 65500
> address-family ipv4 unicast
> network 192.0.2.2/32 route-map rmap
>

Observed output:

> # show bgp ipv4 192.0.2.2/32
> [..]
>     Extended Community: RT:1.0.0.45:55
>

The decoding of the passed cli string assumes this is an
IP address, whereas it is an AS number in dotted format.
Consequently, the vty output will use the ip address encoding.

Count the number of dots in the extended community format.
If a single dot number is detected, the AS format is passed,
and used by the vty output.

After fix:

>
> # show bgp ipv4 192.0.2.2/32
> [..]
>    Extended Community: RT:65581:55
>

For remind, AS 65581 and AS 1.45 are a unique AS number.

> show bgp neighbor
> BGP neighbor is 192.0.2.1, remote AS 65500, local AS 65581, external link
> [..]

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>