nfs: show current proxy-io transfers in the door

Acked-by: Paul Millar
Target: master, 2.11, 2.10
Require-book: no
Require-notes: no
(cherry picked from commit 7e21610e81918a7f3d6ad9d2ec437b53d36db336)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #1181 from kofemann/show-proxyio-2.11

nfs: show current proxy-io transfers in the door