IB/core: Temporarily disable ex_query_device uverb

Commit 5a77abf9

 ("IB/core: Add support for extended query device caps")
added a new extended verb to query the capabilities of RDMA devices, but the
semantics of this verb are still under debate [1].

Don't expose this verb to userspace until the ABI is nailed down.

[1] [PATCH v1 0/5] IB/core: extended query device caps cleanup for v3.19
    http://www.spinics.net/lists/linux-rdma/msg22904.html

Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>