misc: move osi to plugin

misc: move osi to plugin

Type: refactor

This patch moves osi into a plugin, and also modifies
the init functions of llc and snap to preserve init
order dependency (llc_init --> osi_init --> snap_init).

While the initial intent was to move osi/llc/snap together
into a single plugin, there exists a dependency on llc
in vnet/ethernet, which would require further refactoring
and testing work.

Change-Id: Ic0eff030ee29c8d316c0e0fe13931451aa193527
Signed-off-by: Hadi Rayan Al-Sandid <[email protected]>