netd: Add enhanced routing support

Add support for policy and metric based routing APIs to netd. This
functionality is used for WQE, IMS, and Android QoS features.

Combined merge commit for following commits:

(cherry picked from Ia22847dd9611ff16eea25336716d4440461565e0)

netd: add metric support for routing
Add support for adding of cost (metric) of a route.
Changed call to ip from logwrapper to popen to handle errors caught during
a route operation.

netd: Add policy routing functionality to netd
Adding a new class RouteController to handle policy routing (source)
functionality in netd.
Installing a handler in CommandListener to handle policy routing
commands.

netd: Validate input argument for Route commands
Check for valid command line argument that is
passed to RouteController module.
CRs-fixed: 569443

RouteController: use fixed priority for ip rule
Use fixed priority when adding source policy rules
CR-fixed: 613222

Conflicts:
	server/CommandListener.cpp
	server/CommandListener.h

Change-Id: Ic828041d8f5be77a764ce22c45c5091ee8ae6dd2