Add proper kernel support assumption to RateLimitTest

As it turns out, /proc/config.gz can be accessed via shell command from
within a CTS test. This adds a proper kernel support check for the
RateLimitTest.

Bug: 220801455
Test: atest RateLimitTest
Change-Id: I4d3a6848c1c05c313cb74b235294cee982eecf57
1 file changed