Dtrace: add optional size argument to tracemem().

Dtrace: add optional size argument to tracemem().

Merge change from illumos:

1455 DTrace tracemem() should take an optional size argument

Our local enhancements to dt_print_bytes were equivalent to
those in illumos but we made it match the illumos version
to ease further code merges.

For now leave out tst.smallsize.d and tst.smallsize.d.out
since those don't seem to work cleanly on FreeBSD.

This change bumps the DT_VERS_* number to 1.7.1 in accordance
to what is done in illumos.

Illumos Revision:	13457:571b0355c2e3

Reference:
https://www.illumos.org/issues/1455

Tested by:	Fabian Keil
Obtained from:	Illumos
MFC after:	1 month