Reduce NPMS threshold for network restrictions to IMP_FG.

Reducing the threshold from BFGS to IMP_FG to make sure
Expedited jobs are not subject to network restrictions
during power and data saver modes.

Bug: 177641226
Test: atest CtsHostsideNetworkTests:HostsideRestrictBackgroundNetworkTests
Change-Id: I936e4c27710a54f61346234b7999f996acca86a1