dp83640: increase receive time stamp buffer size

The dp83640 buffers receive time stamps from special PHY status frames,
matching them to received PTP packets in a work queue. Because the timeout
for orphaned time stamps is so long and the buffer is so small, the driver
can drop time stamps under moderate PTP traffic.

This commit fixes the issue by decreasing the timeout to (at least) one
timer tick and increasing the buffer size.

Signed-off-by: Richard Cochran <richard.cochran@omicron.at>
Cc: <stable@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>