BUG/MINOR: quic: Missing STREAM frame type updated

BUG/MINOR: quic: Missing STREAM frame type updated

This patch follows this commit which was not sufficient:
  BUG/MINOR: quic: Missing STREAM frame data pointer updates

Indeed, after updating the ->offset field, the bit which informs the
frame builder of its presence must be systematically set.

This bug was revealed by the following BUG_ON() from
quic_build_stream_frame() :
  bug condition "!!(frm->type & 0x04) != !!stream->offset.key" matched at src/quic_frame.c:515

This should fix the last crash occured on github issue #2074.

Must be backported to 2.6 and 2.7.