After searching the whole Internet for 2 days, getting piece of info here and there, this is how I was able to root my Huawei Honor 6C Pro (JMM-L22) successfully:
- Enable Android developer options
- Enable USB debugging and OEM unlock from Android developer options
- From a computer, download Honor 6C Pro stock firmware at http://download-c.huawei.com/download/downloadCenter?downloadId=97622&version=410780&siteCode=ru
- From a computer, download Huawei Update Extractor at https://forum.xda-developers.com/showthread.php?t=2433454
- Start Huawei Update Extractor and open dload/UPDATE.APP from stock firmware
- Right-click BOOT.img and extract it to disk
- Transfer BOOT.img to phone storage
- From phone, download and install MagiskManager APK at https://forum.xda-developers.com/apps/magisk/official-magisk-v7-universal-systemless-t3473445
- Launch MagiskManager, click install, click Patch Boot Image File and select transfered BOOT.img