ubik: Log sync site for SDISK_SendFile USYNC error

ubik: Log sync site for SDISK_SendFile USYNC error

In SDISK_SendFile, we return a USYNC error if the caller is not the
sync site. Say who the sync site is when we do this, to possibly help
post-mortem debugging.

Reviewed-on: https://gerrit.openafs.org/12943
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit c44f6f7a8052bdd1fb021e07bb6ae142b61e6b5b)

Change-Id: I398780c98ee5eade75e06a42d54637c169bc250a
Reviewed-on: https://gerrit.openafs.org/12948
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>