mbuf: use macros only to access metadata
mbuf: use macros only to access metadata

Removed the explicit zero-sized metadata definition at the end of the
mbuf data structure. Updated the metadata macros to take account of this
change so that all existing code which uses those macros still works.

Signed-off-by: Bruce Richardson <66b9e8e8fbd5e9f41f91b0af050876182ce9d0e4@intel.com>
Acked-by: Olivier Matz <dfcc1510895413197abb4336e39bb0a3906cba71@6wind.com>

mixja/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,venkynv/dpdk-mirror,mixja/dpdk,mixja/dpdk,msune/dpdk,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,venkynv/dpdk-mirror,venkynv/dpdk-mirror,msune/dpdk,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,mixja/dpdk,msune/dpdk,msune/dpdk