Current command (bundled two into one) is absolutely wrong.

When you configure TCP session with the source, the command thinks, that
it's a SSH session with a username.

It's much better to split this into two separate commands where it's much
easier to do the changes in the future (if more options comes in).

Yes, this is a breaking change, but there is no other proper way to overcome
this.

Bonus note how it looks, which also can lead to crashes (due to port 0x0):

```
(gdb) p *cache->tr_config.ssh_config
$11 = {host = 0x5555562f9cd0 "1.1.1.1", port = 0, bindaddr = 0x0,
  username = 0x55555629ad00 "",
  server_hostkey_path = 0x7ffff53667a0 <rpki_create_socket> "Uf\017\357\300H\211\345AWAVAUATSH\201", <incomplete sequence \354\230>, client_privkey_path = 0x0,
  data = 0x0, new_socket = 0x51, connect_timeout = 4143762592,
  password = 0x7ffff6fccca0 <main_arena+96> "\300\"0VUU"}
(gdb) p *cache->tr_config.tcp_config
$12 = {host = 0x5555562f9cd0 "1.1.1.1", port = 0x0, bindaddr = 0x0,
  data = 0x55555629ad00, new_socket = 0x7ffff53667a0 <rpki_create_socket>,
  connect_timeout = 0}
```

Signed-off-by: Donatas Abraitis <[email protected]>

SERVER_PUBKEY is not the best name to describe what it really is.

Signed-off-by: Donatas Abraitis <[email protected]>