fsk_attach() sets DN_QHT_HASH in fs->fs.flags when the flowset or its
scheduler has a mask. Userland never sends that flag, so the bcmp() in
config_fs() never matches for such a flowset and re-applying the same
"queue N config ... mask ..." line takes the changed path, which
destroys all queues of the flowset and the packets in them. Firewall
front ends that re-run their dummynet config on every reload hit this.

Take the flag from the existing flowset before the comparison. If the
flowset did change, fsk_attach() computes the flag again.

PR: 298731
Signed-off-by: Abdul Wasey <w453y.me@gmail.com>

• A masked queue (queue 77 config pipe 77 mask dst-ip 0xffffffff weight 10) with a ping through it, then the same line again. The flow queue's packet counter, once a second: stock 7, 43, 83, then 36 after the re-apply (the queue was destroyed); patched 12, 48, 88, then 124, 164, 200 (kept). Changing the weight to 20 still rebuilds it (12).