TM-16: Really skip VLAN header for indexing.

This should solve TM-16 ( https://bro-tracker.atlassian.net/browse/TM-16 ). The problem is that the pointer idxpacket is indeed initialized with correct address of packet start after skipping VLAN header, but it was not used afterwards - original pointer, which includes also VLAN header has been used instead.

However, Tyler ( https://bro-tracker.atlassian.net/secure/ViewProfile.jspa?name=tyler.schoenke ) reported, that time-machine starts to drop lots of packets after applying this patch. I can not see any direct connection between these two things, but I am no time-machine expert after all. Would someone more experienced with this code give some hints on this please? Thx.