Local backend: Fix attributes not added to the right channel

When two channels (one input, one output) shared the same ID,
the global attributes were always added to the first one.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
Local backend: Add scan elements after moving shared attributes

The scan elements are never prefixed with the channel name, so they
were preventing the channel name to be detected from the other
attributes.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
IIOD: Allow the dot character in command parameters

This allows floating-point values to be passed as parameters.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>