datapath: Make it possible to query vports by name regardless of datapath.

datapath: Make it possible to query vports by name regardless of datapath.

Until now it has only been possible to query a vport if you know what
datapath it is on.  This doesn't really make sense, so this commit removes
that restriction.  It is a little bigger than one might naturally expect
because locking changes are required.

This also allows us to get rid of the ETHTOOL_GDRVINFO kluge that has
bothered me for a long time.  The next commit does that.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>