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
diff --git a/bin/crosh b/bin/crosh
index 6f05352..dcc1222 100755
--- a/bin/crosh
+++ b/bin/crosh
@@ -54,6 +54,9 @@
  modem <command> [args...]
   Interact with the 3G modem. Run "modem help" for detailed help.
 
+ modem_set_carrier carrier-name
+  Configures the modem for the specified carrier.
+
  network_logging <wifi | cellular | ethernet>
   A function that enables a predefined set of tags useful for
   debugging the specified device.
@@ -410,6 +413,10 @@
   /usr/bin/modem "$@"
 }
 
+cmd_modem_set_carrier() {
+  /usr/bin/modem_set_carrier "$@"
+}
+
 cmd_set_apn() {
   /usr/bin/set_apn "$@"
 }