bgpd: fix add prefix sent in 'show bgp neighbor'

bgpd: fix add prefix sent in 'show bgp neighbor'

The 'acceptedPrefixCounter' is available in 'show bgp neighbor json', but
there is no equivalent when using the non json output. Add it.

> # show bgp neighbor
> [..]
>  Community attribute sent to this neighbor(all)
>  0 accepted prefixes, 1 sent prefixes

Fixes: 856ca177c4bb ("Added json formating support to show-...-neighbors-... bgp commands.")
Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>