sdig: Increment the DNS message IDs when pipelining

sdig: Increment the DNS message IDs when pipelining

As stated in section 6.2.1 of rfc7766:
  "When sending multiple queries over a TCP connection, clients MUST NOT
   reuse the DNS Message ID of an in-flight query on that connection in
   order to avoid Message ID collisions.  This is especially important
   if the server could be performing out-of-order processing"