IB/core: Fix input len in multiple user verbs

Most user verbs pass user data to the kernel with the inclusion of the
ib_uverbs_cmd_hdr structure. This is problematic because the vendor has
no ideas if the verb was called by a legacy verb or an extended verb.
Also, the incosistency between the verbs is confusing.

Fixes: 565197dd ("IB/core: Extend ib_uverbs_create_cq")
Signed-off-by: Ram Amrani <Ram.Amrani@cavium.com>
Signed-off-by: Ariel Elior <Ariel.Elior@cavium.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>