net: doc: Add missing defgroups to network header files

Some of the networking header files in include/net/ directory were
missing @defgroup doxygen directives.

There was also duplicate @defgroup directives which are now changed
to @addtogroup directives.

Added also missing API links to doc/api/networking.rst file.

Added exceptions to .known-issues/doc/networking.conf file so that
doxygen does not complain.

Jira: ZEP-2308

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
21 files changed