[profiler] Make the default sample frequency 100 Hz.

[profiler] Make the default sample frequency 100 Hz.

Our previous default (1000 Hz) was quite extreme and resulted in very high
overhead from the profiler for moderate workloads.

Also, fix the profiler to actually treat the 'freq' argument as a frequency
when passing it to the runtime. It was being incorrectly treated as a sleep
interval.