Revert "Remove duplicate code from xdp_drop_count.py (#2049)" (#2069)
Revert "Remove duplicate code from xdp_drop_count.py (#2049)" (#2069)

This reverts commit 5b76047f528b56072b541c406103f07589d6efe2.

The code is actually not duplicated. It is used to process
double vlan's. See comments in:
  https://github.com/iovisor/bcc/pull/1493
mcaleavya/bcc,tuxology/bcc,brendangregg/bcc,iovisor/bcc,mcaleavya/bcc,brendangregg/bcc,iovisor/bcc,tuxology/bcc,mcaleavya/bcc,brendangregg/bcc,iovisor/bcc,tuxology/bcc,brendangregg/bcc,tuxology/bcc,mcaleavya/bcc,mcaleavya/bcc,tuxology/bcc,iovisor/bcc,iovisor/bcc,brendangregg/bcc