net: xfrm: revert to lower xfrm dst gc limit

revert c386578f ("xfrm: Let the flowcache handle its size by default.").

Once we remove flow cache, we don't have a flow cache limit anymore.
We must not allow (virtually) unlimited allocations of xfrm dst entries.
Revert back to the old xfrm dst gc limits.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -1291,8 +1291,7 @@ tag - INTEGER
 xfrm4_gc_thresh - INTEGER
 	The threshold at which we will start garbage collecting for IPv4
 	destination cache entries.  At twice this value the system will
-	refuse new allocations. The value must be set below the flowcache
-	limit (4096 * number of online cpus) to take effect.
+	refuse new allocations.
 
 igmp_link_local_mcast_reports - BOOLEAN
 	Enable IGMP reports for link local multicast groups in the
@@ -1778,8 +1777,7 @@ ratelimit - INTEGER
 xfrm6_gc_thresh - INTEGER
 	The threshold at which we will start garbage collecting for IPv6
 	destination cache entries.  At twice this value the system will
-	refuse new allocations. The value must be set below the flowcache
-	limit (4096 * number of online cpus) to take effect.
+	refuse new allocations.
 
 
 IPv6 Update by:

net/ipv4/xfrm4_policy.c

@@ -266,7 +266,7 @@ static struct dst_ops xfrm4_dst_ops_template = {
 	.destroy =		xfrm4_dst_destroy,
 	.ifdown =		xfrm4_dst_ifdown,
 	.local_out =		__ip_local_out,
-	.gc_thresh =		INT_MAX,
+	.gc_thresh =		32768,
 };
 
 static const struct xfrm_policy_afinfo xfrm4_policy_afinfo = {

net/ipv6/xfrm6_policy.c

@@ -286,7 +286,7 @@ static struct dst_ops xfrm6_dst_ops_template = {
 	.destroy =		xfrm6_dst_destroy,
 	.ifdown =		xfrm6_dst_ifdown,
 	.local_out =		__ip6_local_out,
-	.gc_thresh =		INT_MAX,
+	.gc_thresh =		32768,
 };
 
 static const struct xfrm_policy_afinfo xfrm6_policy_afinfo = {