Merge branch 'ptp-virtual-clock-improvements'

Miroslav Lichvar says:

====================
Virtual PTP clock improvements and fix

v2:
- dropped patch changing initial time of virtual clocks

The first patch fixes an oops when unloading a driver with PTP clock and
enabled virtual clocks.

The other patches add missing features to make synchronization with
virtual clocks work as well as with the physical clock.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>