ols: move device context creation from protocol.c to api.c

ols: move device context creation from protocol.c to api.c

The get_metadata() routine was unfortunately named, and surprisingly did
more than its name suggested. Rename the routine to contain the ols_
prefix. Run communication to the device in protocol.c, but keep sdi and
devc creation in api.c where they are expected during maintenance. This
"unhides" where stuff is happening, and eliminates redundancy between
the models which support meta data to announce their features, and other
"compatibles" which are covered by generic fallback data.