lib/test_fprobe: Add a test case for nr_maxactive

lib/test_fprobe: Add a test case for nr_maxactive

Add a test case for nr_maxactive. If the number of active
functions is more than nr_maxactive, it must be skipped.

Link: https://lkml.kernel.org/r/167526698856.433354.4430007340787176666.stgit@mhiramat.roam.corp.google.com
Cc: Florent Revest <revest@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>