Fix for 2 bugs related to TCP Signatures :

• If the peer sends the Signature option in the SYN, use of Timestamps and Window Scaling were disabled (even if the peer supports them).
• The sender must not disable signatures if the option is absent in the received SYN. (See comment in syncache_add()).

Found, Submitted by: Noritoshi Demizu <demizu at dd dot ij4u dot or dot jp>.
Reviewed by: Mohan Srinivasan <mohans at yahoo-inc dot com>.