The inner L2 length returned by rte_net_get_ptype() is not
properly initialized. If the caller does not zero the header
lengths structure, the inner_l2 field will be undefined.
Fix it by initializing inner_l2 to 0 when parsing a inner layer.
Fixes: 2c15c5377d ("net: support NVGRE in software packet type parser")
Cc: stable@dpdk.org
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>