Increase default maximum safe_body function

There is this specific test test_absolute_limits_negative which's xml
version is bigger than 2048 characters and was truncated on tempest.log
that is fixed increasing that maximum even though I'm not sure how long
xml tests will live here.
Closes-Bug: #1383996

Change-Id: I771921e3c14333afc791e21395c0edf9feba5ee0
Merge "Increase default maximum safe_body function"