Properly account for VPN apps that make heavy use of the tun
interface. Prior to this change a VPN app could be incorrectly charged
for more data than it actually used if it sent more traffic through
the tun interface than the underlying interface.
This change excludes VPN app traffic on the tun interface from the
adjustment pool and doesn't redistribute traffic to the VPN app.
Instead all of the redistributed traffic is deducted from the VPN app
which effectively represents any overhead incurred by the VPN app.
BUG: 30557871
(cherry picked from commit 12255e3655)
Change-Id: I06f01aa8fe5fdc06b2d36cfb9c68feb244c2e5de
b135f1d5a8