netfilter: nf_conntrack: use get_unaligned_be32() in tcp_sack()

netfilter: nf_conntrack: use get_unaligned_be32() in tcp_sack()

The timestamp-only fast path dereferences the option stream as
*(__be32 *)ptr, which assumes 4-byte alignment that the TCP option
stream does not guarantee. Use get_unaligned_be32() instead, which
reads the value safely and already returns host byte order, so the
htonl() on the comparison constant can be dropped.

This matches the existing get_unaligned_be32() use later in the same
function.

Assisted-by: Claude:Opus-4.7
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>