genl: Fix genl dumpit() locking.

[ Upstream commit 9b96309c5b0b9e466773c07a5bc8b7b68fcf010a ]

In case of genl-family with parallel ops off, dumpif() callback
is expected to run under genl_lock, But commit def31174
(genl: Allow concurrent genl callbacks.) changed this behaviour
where only first dumpit() op was called under genl-lock.
For subsequent dump, only nlk->cb_lock was taken.
Following patch fixes it by defining locked dumpit() and done()
callback which takes care of genl-locking.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
CC: Jesse Gross <jesse@nicira.com>
CC: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>