selftests: netfilter: correct PKTGEN_SCRIPT_PATHS in nft_concat_range.sh

Before change:
make -C netfilter
 TEST: performance
   net,port                                                      [SKIP]
   perf not supported
   port,net                                                      [SKIP]
   perf not supported
   net6,port                                                     [SKIP]
   perf not supported
   port,proto                                                    [SKIP]
   perf not supported
   net6,port,mac                                                 [SKIP]
   perf not supported
   net6,port,mac,proto                                           [SKIP]
   perf not supported
   net,mac                                                       [SKIP]
   perf not supported

After change:
   net,mac                                                       [ OK ]
     baseline (drop from netdev hook):               2061098pps
     baseline hash (non-ranged entries):             1606741pps
     baseline rbtree (match on first field only):    1191607pps
     set with  1000 full, ranged entries:            1639119pps
ok 8 selftests: netfilter: nft_concat_range.sh

Fixes: 611973c1 ("selftests: netfilter: Introduce tests for sets with range concatenation")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jie2x Zhou <jie2x.zhou@intel.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>