IB/rdmavt: Disable by default

There is a strict policy in the Linux kernel that new drivers must be
disabled by default. Hence leave out the "default m" line from Kconfig.

Fixes: 0194621b ("IB/rdmavt: Create module framework and handle driver registration")
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Jubin John <jubin.john@intel.com>
Cc: Dennis Dalessandro <dennis.dalessandro@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Mike Marciniszyn <mike.marciniszyn@intel.com>
Cc: <stable@vger.kernel.org> # v4.6+
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/sw/rdmavt/Kconfig

 config INFINIBAND_RDMAVT
 	tristate "RDMA verbs transport library"
 	depends on 64BIT
-	default m
 	---help---
 	This is a common software verbs provider for RDMA networks.