ringbuf: Fixes to header files for better understanding
ringbuf: Fixes to header files for better understanding

1. Usage of this module required applications to include additional
files. What files to include is not very intuitive. Instead, it is
better for the header file itself to include other files as required.
2. Even though it may seem logical, it is better to explicitly mention
that an item needs to be "Returned" after a Receive

Signed-off-by: Piyush Shah <22b9c231e86e73b6822f10a284ad53e606c09e6d@espressif.com>

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