Set default HWM in API call as well

@basepi set the HWM to 1000 by default in #8804 and this is a
complementary commit to that one. It is now obvious that the HWM is 1000
by default in the source code.

X-ref: #7662 and #7284
Merge pull request #8885 from holmboe/hwm1000

Set default HWM in API call as well