net: sockets: Allow to build CAN sockets with offloading enabled

There is no releavnce between CAN sockets and offloading that would
prevent one from working with another, therefore it's not right to
allow CAN sockets to be build only if offloading is disabled. Fix the
wrong dependency in socket CMakeLists.txt file.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>