dpdk: remove dead code
dpdk: remove dead code

rte_eth_tx_burst() returns the number of packets  actually stored in
transmit descriptors and the return type is uint16. n_sent cannot be
negative and the if branch is dead code.

Type: improvement

Change-Id: Idc2980d342756c1093ddf74ea6207d072e819331
Signed-off-by: Benoît Ganne <38aad8ffcfa407b890d258e568f161530f66882d@cisco.com>

FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp