ixgbe: fix build with icc

ixgbe: fix build with icc

When using Intel C++ compiler(icc) 14.0.1.106 or the older icc 13.x
version, the mbuf initializer variable was not getting configured
correctly, as the mb_def variable was not set correctly. This is due
to an issue with icc (DPD200249565 which already been fixed in
icc 14.0.2 and newer compiler release) where it incorrectly calculates
the field offsets with initializers when zero-sized fields
are used in a structure.
To work around this, the code in ixgbe_rxq_vec_setup does not setup the
fields using an initializer, but instead assigns the values individually
in code.
NOTE: There is no performance impact to this change as the queue
setup functions are not data-plane APIs, but are only used at app
initialization.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Reviewed-by: David Marchand <david.marchand@6wind.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>