ubik: Protect ubik_servers in urecovery_Interact

ubik: Protect ubik_servers in urecovery_Interact

urecovery_Interact can modify the global ubik_servers structures,
including destroying and recreating the RX connection objects. In the
pthreaded case, DBHOLD the database, so we do not modify the
structures out from under another thread trying to use them.

Change-Id: I62ab7b77e17c65ec8840659957ef6d00303ea5a4
Reviewed-on: http://gerrit.openafs.org/2108
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>