bgpd: Add `debug bgp updates detail` command

bgpd: Add `debug bgp updates detail` command

When filtering with `debug bgp updates in x.x.x.x prefix-list plist`, we want
to filter out unnecessary messages like:

```
127.0.0.1(Unknown) rcvd UPDATE wlen 0 attrlen 20 alen 5
```

Such a line as above will be repeated for all the paths received and it's useless
without knowing the prefix (because NLRIs are not parsed yet).

But want to see only relevant ones:

```
127.0.0.1(Unknown) rcvd UPDATE w/ attr: nexthop 127.0.0.1, origin i, path 65002
127.0.0.1(Unknown) rcvd 10.255.255.1/32 IPv4 unicast
```

With `debug bgp updates detail` we can combine this to something like:

```
127.0.0.1(Unknown) rcvd UPDATE w/ attr: nexthop 127.0.0.1, origin i, path 65002
127.0.0.1(Unknown) rcvd UPDATE wlen 0 attrlen 20 alen 5
127.0.0.1(Unknown) rcvd 10.255.255.1/32 IPv4 unicast
```

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