Update exception type thrown when NetworkStack is missing

rethrowFromSystemServer is throwing DeadSystemException which
is different from the original log message. Thus, update the
way to rethrow the same RemoteException.

Bug: 130028724
Test: atest FrameworksNetTest
Test: Kill NetworkStack and check the log message
Change-Id: I60862e276dd4e2d143278b272a9ba54219acce26
Merged-In: Ic1766e839f8f06b539d5f6cfecd29547021fd1d9
Merged-In: I67005a5384888e8acaf1249af79484e2d5ed6f1f
(cherry picked from commit 7f581219)