Fix netdutils::extract and SliceTest.

netdutils::extract was taking Tail... arguments by value, but the
intention was to take them by reference and populate their memory.

I checked and there are no current calls to the variadic overload
outside of SliceTest.cpp.

Bug: 67431299
Test: modified Android.mk to include SliceTest.cpp in netd_unit_test then runtest -x server/netd_unit_tests.cpp
Change-Id: I6a28970eb0734427fa7a3f21c6a2984df1585ceb
2 files changed