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 <halsandi@cisco.com>
diff --git a/docs/spelling_wordlist.txt b/docs/spelling_wordlist.txt
index f90ffa8..e428390 100644
--- a/docs/spelling_wordlist.txt
+++ b/docs/spelling_wordlist.txt
@@ -805,6 +805,7 @@
 Optimisations
 optimised
 os
+osi
 outacl
 packagecloud
 papi