Add back fowner capability to netd

This addresses error messages like:

11-30 18:00:15.196  6917  6917 W Binder:6596_2: type=1400 audit(0.0:46):
avc: denied { fowner } for capability=3 scontext=u:r:netd:s0
tcontext=u:r:netd:s0 tclass=capability permissive=0

11-30 18:00:15.200  6596  6917 E /system/bin/netd:
android::WriteStringToFile fchmod failed: Operation not permitted

11-30 18:00:15.200  6596  6917 E Netd    : failed to write to
/data/misc/net/rt_tables (Operation not permitted)

Bug: 31147892
Change-Id: Id11704f8e2b8c08db92de374ed44913b70d6ae66