Fix PIA packet replay to deliver copy of IP header

This prevented one from writing a packet-wise analyzer that needs access
to IP headers and can be attached to a connection via signature match.

None of the analyzers currently shipping are affected.  And maybe it's
unlikely there will be many that ever would be, but it's awkward for the
API to omit IP headers in this special case (i.e. packets buffer for use
with DPD signature matching).

Addresses BIT-1298
Change IP_Hdr copy ctor/assign to explicit method

Addresses BIT-1298
Merge remote-tracking branch 'origin/topic/jsiwek/bit-1298'

* origin/topic/jsiwek/bit-1298:
  Change IP_Hdr copy ctor/assign to explicit method
  Fix PIA packet replay to deliver copy of IP header

BIT-1298 #merged