detect: fix multiple files per tx inspect

detect: fix multiple files per tx inspect

Fix the inspection of multiple files in a single TX, where new files
may be added to the TX after inspection started.

Assign the hard coded id DE_STATE_FLAG_FILE_INSPECT to the file
inspect engine.

Make sure that sigs that do file inspection and don't match on the
current file always store a detailed state. This state will include
the DE_STATE_FLAG_FILE_INSPECT flag.

When the app-layer indicates a new file is available, for each sig
that has the DE_STATE_FLAG_FILE_INSPECT flag set, reset part of the
state so that the sig is evaluated again.