sunvnet: make sunvnet common code dynamically loadable

When the sunvnet_common code was split out for use by both sunvnet
and the newer ldmvsw, it was made into a static kernel library, which
limits the usefulness of sunvnet and ldmvsw as loadables, since most
of the real work is being done in the shared code.  Also, this is
simply dead code in kernels that aren't running the LDoms.

This patch makes the sunvnet_common into a dynamically loadable
module and makes sunvnet and ldmvsw dependent on sunvnet_common.

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>