Setting FTP host command works, firmware thinks it failed

The following error occured, even though MQTT login/logout worked and the AT command to set the FTP host works.

Seems to have been caused by already being logged in. A (Wombat) firmware FTP state machine bug?

```
11:36:15.282 > $ ftp login
11:36:17.689 > [ 79887][I][ftp_stack.cpp:30] ftp_login(): [ftp_stack] Starting modem and login
11:36:17.701 > [ 79899][I][CAT_M1.cpp:86] make_ready(): [CAT_M1] already_called = true, early return
11:36:17.708 > AT+CEREG?
11:36:17.708 >
11:36:17.708 > +CEREG: 0,1
11:36:17.708 >
11:36:17.708 > OK
11:36:17.726 > AT+UPSND=0,0
11:36:17.738 >
11:36:17.738 > +UPSND: 0,0,"10.120.32.214"
11:36:17.738 >
11:36:17.738 > OK
11:36:17.738 > [ 79937][I][Utils.cpp:356] connect_to_internet(): [utils] Already connected to internet
11:36:17.751 > AT+UFTP=1,"sherman-pablo.bnr.la"
11:36:17.759 >
11:36:17.759 > OK
11:36:17.759 > [ 79957][E][ftp_stack.cpp:44] ftp_login(): [ftp_stack] Failed to set FTP server hostname
11:36:17.769 >
11:36:17.769 > ERROR
11:36:17.769 > $
```