app/testpmd: fix GTP L2 length in checksum engine

[ upstream commit dd827fa42a30a9b0aa87a1d5614af83ea32b19e0 ]

GTP header can be followed by an optional 32 bits extension.

But, l2_len value statically set to RTE_ETHER_GTP_HLEN
which is defined to be
        (sizeof(struct rte_udp_hdr) + sizeof(struct rte_gtp_hdr))

This fixes the l2_len to take into consideration the extension size.

Fixes: d8e5e69 ("app/testpmd: add GTP parsing and Tx checksum offload")

Signed-off-by: Raslan Darawsheh <rasland@nvidia.com>
Acked-by: Aman Singh <aman.deep.singh@intel.com>

app/test-pmd/csumonly.c

@@ -246,7 +246,7 @@ parse_gtp(struct rte_udp_hdr *udp_hdr,
 		info->l4_proto = 0;
 	}
 
-	info->l2_len += RTE_ETHER_GTP_HLEN;
+	info->l2_len += gtp_len + sizeof(udp_hdr);
 }
 
 /* Parse a vxlan header */