IIOD: Add a "short path" to receive samples instead of muxing

Muxing the samples is only required when there are several clients
sending samples. When only one client is connected, the samples sent by
the one client can be directly stored in the buffer.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
IIOD: Small fix for commit 84689857

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