doc: fix reference to include file
doc: fix reference to include file

fix reference to net/buf.h to include/net/buf.h

Change-Id: I29514b5f48e6f0eefb0ed53185ed3b1de2a2f3f4
Signed-off-by: David B. Kinder <c56c8b29908a5b2af1b63001268d73a0b7f972ba@intel.com>

tidyjiang8/zephyr-doc,tidyjiang8/zephyr-doc,tidyjiang8/zephyr-doc,tidyjiang8/zephyr-doc,tidyjiang8/zephyr-doc