check-sr-results.yaml: parse report.txt only for ir2.1

Starting with IR 2.1 we parse the report.txt and extract the number of
network controller from there.
Massage our rules a bit to do so only for IR 2.1 and not for IR 2.0.

Update the unit test accordingly.

Signed-off-by: Vincent Stehlé <vincent.stehle@arm.com>