[mxio] Add Nlink field to Vnattr

- Also update the list of RIO operations

Change-Id: I1057224b8578905250d30d895b2c75e6912df3dd
diff --git a/src/syscall/mx/mxio/mxio.go b/src/syscall/mx/mxio/mxio.go
index f809073..fc3fae7 100644
--- a/src/syscall/mx/mxio/mxio.go
+++ b/src/syscall/mx/mxio/mxio.go
@@ -160,6 +160,7 @@
 	Mode       Vtype
 	Inode      uint64
 	Size       uint64
+	Nlink      uint64
 	CreateTime uint64
 	ModifyTime uint64
 }
diff --git a/src/syscall/mx/mxio/rio/message.go b/src/syscall/mx/mxio/rio/message.go
index a138119..2ae9c2d 100644
--- a/src/syscall/mx/mxio/rio/message.go
+++ b/src/syscall/mx/mxio/rio/message.go
@@ -62,7 +62,8 @@
 	OpGetAddrInfo
 	OpSetAttr
 	OpSync
-	OpNumOps // The total number of operations
+	OpLink   = uint32(iota) | OpFlagOneHandle
+	OpNumOps = uint32(iota) // The total number of operations
 )
 
 // Ops which correspond to a previously listed operation, but have a different number of handles