juci-voice-client: fix CA certificate upload
This change fixes certificate authority certificate upload through ubus:
- Creates an "ssl" directory if it doesn't exist (otherwise echo fails)
- Disables processing of backslashes while reading JSON data, which used to damage certificate data
Tested on DG400PRIME-A-IOPSYS-4.3.3-191212_1455.y3
.
Edited by Roman Azarenko