ports: add logging to IVSHM port

Log potential issues, such as failure to enqueue mbufs to
IVSHM rings.

Change-Id: I6c651890b22c1f0353909f5405483fccfba9cea7
Signed-off-by: Mark Kavanagh <mark.b.kavanagh@intel.com>
Reviewed-By: Stephen Finucane <stephen.finucane@intel.com>
Reviewed-By: Mark Gray <mark.d.gray@intel.com>
datapath: add debug logging to ovdk_datapath

Log:
- when unable to enqueue alloc mbufs to the alloc ring
- when unable to enqueue control mbufs to the vswitchd reply ring
- when freeing mbufs from the vswitchd control free ring

Change-Id: I8133cdfcf677d3496b39f6a02282750d76f37514
Signed-off-by: Mark Kavanagh <mark.b.kavanagh@intel.com>
Reviewed-by: Mark D. Gray <mark.d.gray@intel.com>