panics when unloading the dummynet and IPFW modules:
- The callout drain function can sleep and should not be called having
a non-sleepable lock locked. Remove locks around "ipfw_dyn_uninit(0)".
- Add a new "dn_gone" variable to prevent asynchronous restart of
dummynet callouts when unloading the dummynet kernel module.
- Call "dn_reschedule()" locked so that "dn_gone" can be set and
checked atomically with regard to starting a new callout.
Reviewed by: hiren
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D3855
c8cfbc066f