detect/iponly: use flow first flags

detect/iponly: use flow first flags

Instead of ip-only specific flags, reuse the FLOW_PKT_TOSERVER_FIRST and
FLOW_PKT_TOCLIENT_FIRST flags.

Fixes false positives on one sided streams that trigger a opposing flow
timeout packet at the flow's end. That pseudo packet would trigger a
match even though it shouldn't.

Ticket: #7521.