protobuf: add SysctlEntry for ipv4/ipv6 sysctl confs or some others

int32 with boolean value in protobuf has the same size with bool,
many sysctls are boolean but we don't lose anything by storing them
in int32, so add only int32 and string fields

will need string field for stable_secret ipv6 sysctl

also such fromat allows us to easily handle non-present int sysctls
we can check if we have it using has_*arg

v3: rebase images/Makefile to criu-dev branch
v4: use enum for type
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Reviewed-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

images/Makefile

@@ -58,6 +58,7 @@ proto-obj-y	+= opts.o
 proto-obj-y	+= seccomp.o
 proto-obj-y	+= binfmt-misc.o
 proto-obj-y	+= time.o
+proto-obj-y	+= sysctl.o
 
 CFLAGS		+= -iquote $(obj)/
 

images/netdev.proto

 import "opts.proto";
 import "tun.proto";
+import "sysctl.proto";
 
 enum nd_type {
 	LOOPBACK	= 1;
@@ -31,9 +32,14 @@ message net_device_entry {
 	optional bytes address		= 7;
 
 	repeated int32 conf		= 8;
+
+	repeated sysctl_entry conf4	= 9;
 }
 
 message netns_entry {
 	repeated int32 def_conf		= 1;
 	repeated int32 all_conf		= 2;
+
+	repeated sysctl_entry def_conf4	= 3;
+	repeated sysctl_entry all_conf4	= 4;
 }

images/sysctl.proto

+enum SysctlType {
+	__CTL_STR	= 5;
+	CTL_32		= 6;
+}
+
+message sysctl_entry {
+	required SysctlType type	= 1;
+
+	optional int32 iarg		= 2;
+	optional string sarg		= 3;
+}