gbsim/loopback_test: fix test name selection
gbsim/loopback_test: fix test name selection

strstr is being used to match the name of the test, a positive match is
non-null. We'll select the wrong type of test, testing for NULL.

Signed-off-by: Bryan O'Donoghue <165dc05575478af93ac2f97f67be6e1756010094@linaro.org>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@google.com>

gregkh/gbsim,projectara/gbsim,projectara/gbsim,gregkh/gbsim