RouteController: use fixed priority for ip rule

Use fixed priority when adding source policy rules

CR-fixed: 613222
Change-Id: I3182777db6b665c6adc94f65e91b429aac733875
netd: Use append to add routes to secondary routing table

Use <ip route append> instead of <ip route add>
to add routes to the secondary routing table. This
is because adding a route with same v6 address but
different device name fails by using <ip route add>

CRs-Fixed: 618837
Change-Id: Id880e1a155856a5a3afad75135091a17ace07414
Netd: Do not reset routing policies

Stop flushing of all routing policies when resetting to default rule
configuration. This is detrimental to other policy routes set on the
system and creates a conflict. Tethering related rules are already
removed by NatController so this step is unnecessary.

Change-Id: Id9026c089262e37fffe6e5db8eb8e0ccf3338c94
Move VPN routing decisions from iptables to ip

Routes are now encoded by ip rules that send connections to the Vpn
table if the connection is marked and the destination falls into a
route. This differs from the previous design where a mark meant that
the connection must go over the VPN, now a mark simply means that it
may.
Bug: 12549060
Change-Id: I9be7e27a0f46858f109d8bc5c5bced309b05201a
Merge tag 'android-4.4.3_r1' into HEAD

Android 4.4.3 release 1