unix: support Linux NFC Subsystem

This adds the constants and types needed for the Linux NFC Subsystem.
It also adds support for sockaddr_nfc and sockaddr_nfc_llcp to Connect.

The Linux NFC Subsystem is documented in:
https://www.kernel.org/doc/html/latest/networking/nfc.html.

Change-Id: Ic6a79afdba85e9b154ec46f191f27714b4b38a57
Reviewed-on: https://go-review.googlesource.com/c/sys/+/323551
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/unix/syscall_linux_mips64x.go b/unix/syscall_linux_mips64x.go
index 06dec06..27aee81 100644
--- a/unix/syscall_linux_mips64x.go
+++ b/unix/syscall_linux_mips64x.go
@@ -217,6 +217,10 @@
 	cmsg.Len = uint64(length)
 }
 
+func (rsa *RawSockaddrNFCLLCP) SetServiceNameLen(length int) {
+	rsa.Service_name_len = uint64(length)
+}
+
 func InotifyInit() (fd int, err error) {
 	return InotifyInit1(0)
 }