p54: 32-bit tsf timestamps

p54: 32-bit tsf timestamps

tcpdump:
02:15:42.874518 61112184us tsft 48.0 Mb/s 2437 MHz (0x0480) antenna 1 [0x0000000e] CF +QoS Data IV
02:15:42.874557 >>>4356079526us<<< tsft 24.0 Mb/s 2437 MHz (0x0480) antenna 1 [0x0000000e] Acknowledgment
02:15:42.976844 61214513us tsft 1.0 Mb/s 2437 MHz (0x0480) antenna 0 [0x0000000e] Beacon

as one can see on the huge jump, it's very plausible that firmware does not report the
full 64-bit mac time, just the lower 32bit and some kinds of flags...
Therefore if we want a useful timestamp we have to emulate the high bits.

Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>