restore control_input
restore control_input

Summary: I accidentally landed in D4327024 the control_input disable for NCCL. This empirically increases likelihood of deadlocks, although gives a nice perf boost. But better to disable before NVIDIA fixes their stuff.

Reviewed By: Yangqing

Differential Revision: D4338537

fbshipit-source-id: d43efb45965a88bcfe38e5f1dc16c04463e2e038

bwasti/caffe2,davinwang/caffe2,Yangqing/caffe2,pietern/caffe2,pietern/caffe2,Yangqing/caffe2,bwasti/caffe2,xzturn/caffe2,caffe2/caffe2,sf-wind/caffe2,pietern/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2,sf-wind/caffe2,Yangqing/caffe2,davinwang/caffe2,davinwang/caffe2,pietern/caffe2,bwasti/caffe2,bwasti/caffe2,xzturn/caffe2,Yangqing/caffe2,sf-wind/caffe2,davinwang/caffe2,pietern/caffe2,davinwang/caffe2,xzturn/caffe2,bwasti/caffe2,sf-wind/caffe2,sf-wind/caffe2