[TCP]: sysctl to allow TCP window > 32767 sans wscale

Back in the dark ages, we had to be conservative and only allow 15-bit
window fields if the window scale option was not negotiated.  Some
ancient stacks used a signed 16-bit quantity for the window field of
the TCP header and would get confused.

Those days are long gone, so we can use the full 16-bits by default
now.

There is a sysctl added so that we can still interact with such old
stacks

Signed-off-by: Rick Jones <rick.jones2@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/sysctl.h

@@ -402,6 +402,7 @@ enum
 	NET_IPV4_IPFRAG_MAX_DIST=112,
  	NET_TCP_MTU_PROBING=113,
 	NET_TCP_BASE_MSS=114,
+	NET_IPV4_TCP_WORKAROUND_SIGNED_WINDOWS=115,
 };
 
 enum {