unix: add AF_IUCV and SockaddrIUCV

On z series machines the IUCV address family is used to communicate
between parts of the machine and other VMs that may be running.

This adds support for addressing these services using AF_IUCV.

Fixes golang/go#40826

Change-Id: I3aba3beb5cb98d9c548d7abc874ca86fb25c8a52
GitHub-Last-Rev: b964d186b45dd907f4ae302ea9b1ff63e3592eb6
GitHub-Pull-Request: golang/sys#76
Reviewed-on: https://go-review.googlesource.com/c/sys/+/248777
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/linux/types.go

@@ -257,6 +257,16 @@ struct my_sockaddr_un {
 #endif
 };
 
+// copied from /usr/include/netiucv/iucv.h modified with explicit signed chars.
+struct sockaddr_iucv {
+	sa_family_t siucv_family;
+	unsigned short siucv_port;
+	unsigned int siucv_addr;
+	signed char siucv_nodeid[8];
+	signed char siucv_user_id[8];
+	signed char siucv_name[8];
+};
+
 #ifdef __ARM_EABI__
 typedef struct user_regs PtraceRegs;
 #elif defined(__aarch64__)
@@ -540,6 +550,8 @@ type RawSockaddrL2TPIP C.struct_sockaddr_l2tpip
 
 type RawSockaddrL2TPIP6 C.struct_sockaddr_l2tpip6
 
+type RawSockaddrIUCV C.struct_sockaddr_iucv
+
 type RawSockaddr C.struct_sockaddr
 
 type RawSockaddrAny C.struct_sockaddr_any
@@ -594,6 +606,7 @@ const (
 	SizeofSockaddrTIPC      = C.sizeof_struct_sockaddr_tipc
 	SizeofSockaddrL2TPIP    = C.sizeof_struct_sockaddr_l2tpip
 	SizeofSockaddrL2TPIP6   = C.sizeof_struct_sockaddr_l2tpip6
+	SizeofSockaddrIUCV      = C.sizeof_struct_sockaddr_iucv
 	SizeofLinger            = C.sizeof_struct_linger
 	SizeofIovec             = C.sizeof_struct_iovec
 	SizeofIPMreq            = C.sizeof_struct_ip_mreq