dpdk TestPMD foward-mode=txonly

[williamtu]

it's better to have a feature that can modify src ip / dst ip at txonly.c

diff --git a/app/test-pmd/txonly.c b/app/test-pmd/txonly.c
index aed820f5d3..104b3beb6d 100644
--- a/app/test-pmd/txonly.c
+++ b/app/test-pmd/txonly.c
@@ -45,8 +45,8 @@ uint16_t tx_udp_src_port = 9;
 uint16_t tx_udp_dst_port = 9;

 /* use RFC5735 / RFC2544 reserved network test addresses */
-uint32_t tx_ip_src_addr = (198U << 24) | (18 << 16) | (0 << 8) | 1;
-uint32_t tx_ip_dst_addr = (198U << 24) | (18 << 16) | (0 << 8) | 2;
+uint32_t tx_ip_src_addr = (172U << 24) | (31 << 16) | (18 << 8) | 127;
+uint32_t tx_ip_dst_addr = (172U << 24) | (31 << 16) | (25 << 8) | 152;

 #define IP_DEFTTL  64   /* from RFC 1340. */