use simple zero initializers

use simple zero initializers

To initialize a structure with zeros, one field was explicitly set
to avoid "missing initializer" bug with old GCC (e.g. 4.4).
This warning is now disabled (commit <insertlater>) for old versions of GCC,
so the workarounds may be removed.

These initializers should not be needed for static variables but they
are still used to workaround an ICC bug (see commit b2595c4aa92d).

There is one remaining exception where {0} initializer doesn't work cleanly,
even with recent GCC:
lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c:735:9:
error: missing braces around initializer [-Werror=missing-braces]
  struct rte_mbuf mb_def = {0}; /* zeroed mbuf */

Tested with gcc-4.4.7 (CentOS), gcc-4.7.2 (Debian), gcc-4.9.2 (Arch),
clang-3.6.0 and icc-13.1.1.

Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Tested-by: Thomas Monjalon <thomas.monjalon@6wind.com>
Tested-by: John McNamara <john.mcnamara@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
Acked-by: Vlad Zolotarov <vladz@cloudius-systems.com>