datapath: Merge vport "attach" into "create" and "detach" into "destroy".

datapath: Merge vport "attach" into "create" and "detach" into "destroy".

These steps are sequentially in lockstep, so we might as well combine them.

This expands the region over which the vport_lock is held.  I didn't
carefully verify that this was OK.

This also eliminates the synchronize_rcu() call from destruction of tunnel
vports, since they didn't appear to me to need it.

It should be possible to eliminate the synchronize_rcu() from the netdev,
patch, and internal_dev vports, but this commit does not do that.

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