vol: make vol-bless buildable again

vol: make vol-bless buildable again

The vol-bless utility is not built by default and so is subject to
bit-rot.  Thus commit 170dbb3ce301329ff127bb23fb588db31439ae8d 'rx: Use
opr queues' overlooked vol-bless.c when adding includes for users of
struct rx_queue.

Add the required #include <rx/rx_queue.h> so vol-bless builds again.

Note to maintainers: this change is only required for 1.8.x and later;
vol-bless builds fine in 1.6.x and earlier releases.

Change-Id: Ia0bb78e3e7dd74b2f65ac07707aced2c81aaa5d9
Reviewed-on: https://gerrit.openafs.org/14462
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>