vnet_classify: Handle non-aligned vectors and various bugfixes

vnet_classify: Handle non-aligned vectors and various bugfixes

classifier used to crash when packet data was not aligned.
This commit also includes:
- writer lock initialization bugfix
- CLI help was missing opaque-index
- ip_input_acl was applying the mask on buffer->data instead of packet head

On a side note, my tests failed to show any improvements
when using SSE. Further tests might be interesting to see if they
actually perform better.

Change-Id: Ic34eecd6a2226919121ffce2fe4324506deee52f
Signed-off-by: Pierre Pfister <ppfister@cisco.com>