Set the rlimit for unit tests

If the device does not have a sufficient global rlimit set, the unit
tests will fail because it cannot create test maps. Since the unit tests
are usually running as root, let them manually set the rlimit before the
test start to prevent the failure.

Bug: 119279144
Bug: 129246448
Test: netd_unit_test, libnetdbpf_test
Change-Id: Ia882809eee2ddf9d0e0d41cfffa754366962db3d
Merged-In: Ia882809eee2ddf9d0e0d41cfffa754366962db3d
(Cherry-picked from commit ef01d8dc)