Move modem_set_carrier to crosh from crosh-workarounds

BUG=chromium-os:13312
TEST=installed, and ran modem_set_carrier from crosh.  Verified help output looks right.

Review URL: http://codereview.chromium.org/6718007

Change-Id: I39ae0306212ad9d60b2802f60b6abf4ae8d7a1ce
(cherry picked from commit ae24766bed002600c100e82ddf65a216ca935a30)

Review URL: http://codereview.chromium.org/6725009
1 file changed