unix: add Linux Kernel Connection Multiplexor types and constants

For details on KCM, see:
https://www.kernel.org/doc/Documentation/networking/kcm.txt.

Change-Id: I14ebf0aaad17f5a9078f027bd50e050c69b08981
Reviewed-on: https://go-review.googlesource.com/c/sys/+/348449
Trust: Matt Layher <mdlayher@gmail.com>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/zerrors_linux.go

@@ -1286,6 +1286,8 @@ const (
 	IUTF8                                       = 0x4000
 	IXANY                                       = 0x800
 	JFFS2_SUPER_MAGIC                           = 0x72b6
+	KCMPROTO_CONNECTED                          = 0x0
+	KCM_RECV_DISABLE                            = 0x1
 	KEXEC_ARCH_386                              = 0x30000
 	KEXEC_ARCH_68K                              = 0x40000
 	KEXEC_ARCH_AARCH64                          = 0xb70000
@@ -2458,6 +2460,9 @@ const (
 	SIOCGSTAMPNS                                = 0x8907
 	SIOCGSTAMPNS_OLD                            = 0x8907
 	SIOCGSTAMP_OLD                              = 0x8906
+	SIOCKCMATTACH                               = 0x89e0
+	SIOCKCMCLONE                                = 0x89e2
+	SIOCKCMUNATTACH                             = 0x89e1
 	SIOCOUTQNSD                                 = 0x894b
 	SIOCPROTOPRIVATE                            = 0x89e0
 	SIOCRTMSG                                   = 0x890d