Revert r269404 and use cpu_ticks() for dbuf allocation.

Encode CPU's number by XOR'ing the CPU ID against the 64-bit cpu_ticks().

Reviewed by:	mav, gibbs
Differential Revision: https://phabric.freebsd.org/D521
MFC after:	2 weeks
Do not retry token errors. They are not going to disappear by themselves.

MFC after:	1 week