switching from safe to normal modes.
This way both keep-alive safety network implementation and virtual
(testing mode) could co-exists together.

See merge request !29

See merge request nexedi/osie!28

See merge request nexedi/osie!27

See merge request nexedi/osie!26

See merge request nexedi/osie!25

coupler exposes only 2 in the information mode.
Thus until we extend information mode be consistent here, too.

This reverts commit f20868bb.

we support only two I2C slaves thus be consistent here, too.