Fix: detaches the attached XDP/BPF program before af_xdp test run

When call create af_xdp interface api, it will load default xdp program
(xsk_def_prog.o) on the NIC interface, the program will be unloaded
when call delete af_xdp interface api, but current csit config did not
call delete api for af_xdp test cases, that will cause af_xdp test case
fails to run on Intel E810 NIC when the interface already have xdp program
attached, so this patch is to fix this issue by to detach any attached
XDP/BPF program on the interface before af_xdp test case run.

Signed-off-by: Yulong Pei <yulong.pei@intel.com>
Change-Id: I1a557b4c4a7e88c5715cec771a001df29ac4ae6f
Signed-off-by: Yulong Pei <yulong.pei@intel.com>