lib: Lower precedence for ASNUM_TKN when using together with IPV4/IPV6_TKN

lib: Lower precedence for ASNUM_TKN when using together with IPV4/IPV6_TKN

When using together with IPV4/IPV6_TKN, this breaks an existing command like:

```
donatas-pc# clear bgp ipv6 unicast 2a02::1
% Ambiguous command: clear bgp ipv6 unicast 2a02::1
donatas-pc#
```

With this fix:

```
donatas-pc# clear bgp ipv6 unicast 2a02::1
% BGP: Unknown neighbor - "2a02::1"
donatas-pc# clear bgp ipv6 unicast 2.2
% BGP: No IPv6 Unicast peer is configured with AS 2.2
donatas-pc# clear bgp ipv6 unicast 123
% BGP: No IPv6 Unicast peer is configured with AS 123
donatas-pc# clear bgp ipv4 unicast 127.0.0.1
donatas-pc#
```

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>