ethdev: group constant definitions in Doxygen
ethdev: group constant definitions in Doxygen

A lot of flags are parts of a group but are documented alone.
The Doxygen syntax @{ and @} for grouping is used
to make flags appear together and have a common description.

Some Rx/Tx offload flags and RSS definitions are not grouped
because they need to be all properly documented first.

Signed-off-by: Thomas Monjalon <5f50a84c1fa3bcff146405017f36aec1a10a9e38@monjalon.net>
Acked-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>
Acked-by: Andrew Rybchenko <4155e7bf8e0185127625dac6d84336299844982f@oktetlabs.ru>
Acked-by: Kevin Traynor <1f46c93815774a2e602547cf1e37c682d62b566d@redhat.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk