samsung: Update and re-enable plugin for Samsung Y3300/Y3400 modems.

This CL updates the plugin for Samsung Y3300/Y3400 modems to make it
compatible with the changes in upstream ModemManager [1], and then
re-enables it.

[1] http://cgit.freedesktop.org/ModemManager/ModemManager/commit/?id=caeeae27219a91384fa41ac5a1e0f21e1edbaa76

BUG=chromium-os:30744
TEST=Build modemmanager-next

Change-Id: Ibc1f5400255c546813e8009325e034d29bc12be8