shill: Implement a basic IPConfig class.

Different IP configuration types will inherit from that class -- e.g., DHCP
clients, PPP, etc.

BUG=chromium-os:15953
TEST=unit test

Change-Id: Id6ba4559afdf0b10dac43fed55ab51d272aeb4df
Reviewed-on: http://gerrit.chromium.org/gerrit/1852
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
6 files changed