i2o: core: implemented i2o_select_channel.

i2o_select_channel is an internal library function to select the right
channel for a transmission. The channel is selected based on a given
mode.

!NOTE! right now not more then 1 mode should be passed to this function.
If you do, it might not return the channel you are actually looking for,
resultingin errors later on.

Signed-off-by: Michel Megens <dev@michelmegens.net>