Drivers: hv: vmbus: Increase the limit on the number of pfns we can handle

Increase the number of PFNs we can handle in a single vmbus packet.
Some network packets may have more PFNs than the current limit we have.
This is not a bug and this patch can be applied to the *next tree.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>