unix: add anyToSockaddrGOOS on dragonfly

CL 264638 forgot to add func anyToSockaddrGOOS on dragonfly which breaks
the build.

Change-Id: I35d28a972c8c541dea8db0349b7e1440f5ec2fd7
Reviewed-on: https://go-review.googlesource.com/c/sys/+/265377
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>
diff --git a/unix/syscall_dragonfly.go b/unix/syscall_dragonfly.go
index bed7dcf..842ab5a 100644
--- a/unix/syscall_dragonfly.go
+++ b/unix/syscall_dragonfly.go
@@ -47,6 +47,10 @@
 	raw    RawSockaddrDatalink
 }
 
+func anyToSockaddrGOOS(fd int, rsa *RawSockaddrAny) (Sockaddr, error) {
+	return nil, EAFNOSUPPORT
+}
+
 // Translate "kern.hostname" to []_C_int{0,1,2,3}.
 func nametomib(name string) (mib []_C_int, err error) {
 	const siz = unsafe.Sizeof(mib[0])