luci-proto-qmi: allow v6apn and (v6)profile configuration

To support split-APN dual-stack connections over QMI, add new parameters
supported in UCI to LuCI as well. Previously, connection profile wasn't
configurable from LuCI at all, so add options to set which APN profile
to match for each protocol.

Signed-off-by: Lech Perczak <lech.perczak@gmail.com>