airbase-ng: fix -X (hidden SSID)

[gemesa]

Fixes #1139
Fixes #1695

With this change when -X option is supplied the ESSID of the airbase-ng AP is hidden (<length: 1>). I am no 802.11 expert, is this how it should work (see below)?

Before:

$ sudo ./airbase-ng -X -y -W 1 -e "AP" wlp0s20f0u1u2 -a 12:34:56:78:90:AB
20:44:56  Created tap interface at0
20:44:56  Trying to set MTU on at0 to 1500
20:44:56  Access Point with BSSID 12:34:56:78:90:AB started.

$ sudo ./airodump-ng wlan0mon --encrypt WEP
 CH  1 ][ Elapsed: 6 s ][ 2023-02-13 20:44 ][ Are you sure you want to quit? Press Q again to quit.

 BSSID              PWR  Beacons    #Data, #/s  CH   MB   ENC CIPHER  AUTH ESSID
                   
 12:34:56:78:90:AB    0       12        0    0   1   54   WEP  WEP         AP

After:

$ sudo ./airbase-ng -X -y -W 1 -e "AP" wlp0s20f0u1u2 -a 12:34:56:78:90:AB
20:34:29  Created tap interface at0
20:34:29  Trying to set MTU on at0 to 1500
20:34:29  Access Point with BSSID 12:34:56:78:90:AB started.

$ sudo ./airodump-ng wlan0mon --encrypt WEP
 CH  8 ][ Elapsed: 12 s ][ 2023-02-13 20:34 ][ Are you sure you want to quit? Press Q again to quit.

 BSSID              PWR  Beacons    #Data, #/s  CH   MB   ENC CIPHER  AUTH ESSID
                           
 12:34:56:78:90:AB   -1       46        0    0   1   54   WEP  WEP         <length:  1> 

---

$ sudo ./airbase-ng -X -W 1 -e "AP" wlp0s20f0u1u2 -a 12:34:56:78:90:AB 
20:34:10  Created tap interface at0
20:34:10  Trying to set MTU on at0 to 1500
20:34:10  Access Point with BSSID 12:34:56:78:90:AB started.

$ sudo ./airodump-ng wlan0mon --encrypt WEP
 CH  6 ][ Elapsed: 6 s ][ 2023-02-13 20:34 ][ Are you sure you want to quit? Press Q again to quit.

 BSSID              PWR  Beacons    #Data, #/s  CH   MB   ENC CIPHER  AUTH ESSID
                        
 12:34:56:78:90:AB  -28       40        0    0   1   54   WEP  WEP         <length:  1>

---

$ sudo ./airbase-ng -W 1 -e "AP" wlp0s20f0u2 -a 12:34:56:78:90:AB   
21:05:26  Created tap interface at0
21:05:26  Trying to set MTU on at0 to 1500
21:05:26  Access Point with BSSID 12:34:56:78:90:AB started.

$ sudo ./airodump-ng wlan0mon --encrypt WEP
 CH 10 ][ Elapsed: 0 s ][ 2023-02-13 21:05 ][ Are you sure you want to quit? Press Q again to quit.

 BSSID              PWR  Beacons    #Data, #/s  CH   MB   ENC CIPHER  AUTH ESSID

 12:34:56:78:90:AB  -60       13        0    0   1   54   WEP  WEP         AP