You can almost sense the intention behind Codeslinger not being applicable to Control Device at all ("The character is adept at performing a particular Matrix action...This can only be selected for Matrix Actions (p. 237) that have a test associated with them.") but they didn't quite follow through enough.
Let's say you argue:
1. "Control Device" does not have a test associated with it; the action being directed is the action with which the test is associated. You cannot take Codeslinger (Control Device).
1A. "Control Device" has a test associated with it only when the directed action does not. You can take Codeslinger (Control Device) but it applies only to those actions that explicitly use the Control Device test.
2. A jumped-in rigger can "treat Vehicle actions the same way you treat Matrix actions" but that does not cause them to become Matrix actions, as you can "treat" any thing in the same way you "treat" any other thing, and this does not change either thing. You cannot take Codeslinger (Vehicle Action).
2A. In response to getting "any bonus you get to Matrix actions also apply to Vehicle actions when you’re jumped in," since Codeslinger counts as "any bonus" then you can take Codeslinger (Vehicle Action), which is not the same as taking Codeslinger (Control Device).
3. The description for "Codeslinger" explicitly limits the Matrix Actions to which it may apply to those Matrix actions described starting on page 237, i.e., "first-class" Matrix actions, which implicitly excludes any other actions that may through some circumstance happen to be taken in the Matrix. You cannot take Codeslinger (Vehicle Action).
3A. The description for the control rig describes the rigger's VR experience as fundamentally different to a decker's such that there is no room for the kind of higher-level aptitude described by the Codeslinger quality to apply to the instinctual full-body VR of a jumped-in rigger, i.e., the rigger is taking actions, not writing code. You cannot take Codeslinger (Vehicle Action).
I think 1 and 1A can be independently true; either 2 or 2A can be provisionally true; 2A can be true only if you reject the premise of 3 and/or 3A.