Set SSID and PASSPHRASE values from standard input

- SSID is the first line
- PASSPHRASE is the second line

Rationale:
Passing especially passphrase as program argument poses a security issue that the passphrase is visible when doing process listing. Passing it as an environment variable is also not ideal. I did this small patch so when the program is started with the pipe attached to the standard input it will read 2 lines with semantic as described above.

This is how I run it:
gpg -d ~/.netap.gpg | sudo create_ap wlan0 eth0