vxlan: remove judgement with always true
vxlan: remove judgement with always true

if ((A | B) == false)  it means both A and B are false, so for
the following code

if (PREDICT_FALSE (!good_udp1))
      {
        if ((flags1 & VNET_BUFFER_F_L4_CHECKSUM_COMPUTED) == 0)
          {
              ...
          }
      }
if ((flags1 & VNET_BUFFER_F_L4_CHECKSUM_COMPUTED) == 0) is always
true if the code run it. Remove it.

Type: improvement

Signed-off-by: Zhiyong Yang <fbdb847fac8e5e50b588eb93d9ff9fd811b7568c@intel.com>
Change-Id: I6bd1e9340c7a00089fc1c9ae49773add832d309e

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