drbd: re-add lost conf_mutex protection in drbd_set_role
drbd: re-add lost conf_mutex protection in drbd_set_role

The conf_update mutex used to be held while clearing the
net_conf->discard_my_data flag inside drbd_set_role.

It was moved into drbd_adm_set_role with
    drbd: allow parallel promote/demote actions
but then replaced at that location by the newly introduced adm_mutex with
    drbd: Fix a potential deadlock in drbdsetup, introduce resource->adm_mutex

And I simply forgot to put it back in at the original location.

Signed-off-by: Philipp Reisner <35a55a4ac466b5abd81eb66f3f7d6a972dd0dc24@linbit.com>
Signed-off-by: Lars Ellenberg <31df9cacdc65c624cc60c2dcd22bbf92dc230e16@linbit.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs