gfapi: use different name for GETSPEC callback than the one used by glusterfsd

Change-Id: Ibd5be1e1080f9da4ac1fb9112538b3320ef2ff28
BUG: 1174205
Signed-off-by: Raghavendra Bhat <raghavendra@redhat.com>
Reviewed-on: http://review.gluster.org/9277
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>