* sshmngr uci is deprecated and so are the library functions
related to managing that uci, sshmngr will directly interact
with the backend uci now
* a compile time flag is introduced which tells sshmngr code
whether dropbear backend is being used or not
if backend uci is changed then restarting sshmngr can lead to
those changes being lost, try to preserve some of the changes
the following behaviour has been tested:
* if an extra option is set in backend UCI which is not set in
sshmngr UCI for the same section, it will stay as it is
* manually added section in backend is not over-written
* sshmngr managed sections are properly added/modified/deleted
* option BbfSection is introduced which can be set to 0 to prevent
sshmngr from modifying a backend section
the above works except for first boot (then sshmngr will override
backend UCI)
Make the backend daemon configurable, please note, still need
to disable dropbear as default in config and choose the backend
based on config in sshmngr
