rtnl: reset calcit fptr in rtnl_unregister()

rtnl: reset calcit fptr in rtnl_unregister()

commit f567e950bf51290755a2539ff2aaef4c26f735d3 upstream.

To avoid having dangling function pointers left behind, reset calcit in
rtnl_unregister(), too.

This is no issue so far, as only the rtnl core registers a netlink
handler with a calcit hook which won't be unregistered, but may become
one if new code makes use of the calcit hook.

Fixes: c7ac8679bec9 ("rtnetlink: Compute and store minimum ifinfo...")
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>