Use standard vendor/device id detection mechanisms and handle the
net port like other net ports are handled, by just claiming it. Also
reject CDMA modems for now.
BUG=chrome-os-partner:2394
TEST=gmerge modemmanager, watch logs, see detected as Samsung modem, connect to AT&T network
Review URL: http://codereview.chromium.org/6614026
Patch from Jun Woo Lee <jw86.lee@samsung.com>.
Change-Id: I913628ff4a1cd16c8180e3c808644b0134e69e31