brcompatd: Make bridge ioctls synchronous again.

brcompatd: Make bridge ioctls synchronous again.

Before OVSDB was adopted in the vswitch, bridge ioctls were synchronous.
That is, an operation that, say, creates a new bridge was guaranteed to
have completed before brcompatd returned a success result to the kernel.

When OVSDB was adopted, however, we failed to maintain this property.
Instead, bridge creation (etc.) only happened some time after the return
value was passed back to the kernel.  This causes a race condition against
software that creates or deletes bridges or ports and expects that the
operation is completed synchronously.

This commit restores the synchronous behavior.

Bug #2443.