Decrease flaky test rate for BinderTest#BandwidthSetGlobalAlert

It is caused by that FW calls bandwidthSetGlobalAlert during
test running.
Enlarge the testAlertBytes size to decrease flaky rate.

Fail log:
05-26 18:27:28.476   817   817 I netd    : bandwidthSetGlobalAlert(2097149) <0.31ms> <-- called by test
05-26 18:27:28.492   817   817 I netd    : bandwidthSetGlobalAlert(2097152) <0.45ms> <-- called by FW
05-26 18:27:28.494   817   817 I netd    : bandwidthSetGlobalAlert(2097152) <0.45ms> <-- called by test

system/netd/tests/binder_test.cpp:1496: Failure
Expected: (quotaBytes) >= (std::stol(Trim(result))), actual: 2097149 vs 2097152

Bug: 133818065
Test: cd system/netd && atest
Change-Id: I4f016d88b1f521af739b2e13c433fe911a1ba602