netconf: update build to use sysrepo 0.7.5, libyang 0.16-r1
The fixes Francis submitted to sysrepo are now released. We can move to release versions: sysrepo 0.7.5, libyang 0.16-r1.
We need to update build instructions.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information