Revert "Revert "Add NETLINK_ROUTE processing to the netlink client code, so that Ethernet""

This reverts commit 1d504eeb.

Conflicts:

	libsysutils/src/NetlinkEvent.cpp

Bring back the changes from Stan Chesnutt regarding adding NETLINK_ROUTE
processing.  The original commit message description was:

    Add NETLINK_ROUTE processing to the netlink client code, so that Ethernet
    physical-layer up/down events can be tracked.  Upper layers will use these
    events to enable/disable Ethernet connectivity.

The original change was reverted due to an incompatiblity with Motorola's
ril.so binary.  I'll submit a patch to workaround that incompatiblity
separately.

Change-Id: I4e97ac98833b10543e654c63ecae3b9b8c7db44f
Signed-off-by: Mike J. Chen <mjchen@google.com>