Implement CreateMailslot using NtCreateMailslotFile.

diff --git a/include/winternl.h b/include/winternl.h
index 7a6a2d6..320b1ab 100644
--- a/include/winternl.h
+++ b/include/winternl.h
@@ -1424,6 +1424,7 @@
 NTSTATUS  WINAPI NtCreateFile(PHANDLE,ACCESS_MASK,POBJECT_ATTRIBUTES,PIO_STATUS_BLOCK,PLARGE_INTEGER,ULONG,ULONG,ULONG,ULONG,PVOID,ULONG);
 NTSTATUS  WINAPI NtCreateIoCompletion(PHANDLE,ACCESS_MASK,POBJECT_ATTRIBUTES,ULONG);
 NTSTATUS  WINAPI NtCreateKey(PHKEY,ACCESS_MASK,const OBJECT_ATTRIBUTES*,ULONG,const UNICODE_STRING*,ULONG,PULONG);
+NTSTATUS  WINAPI NtCreateMailslotFile(PHANDLE,ACCESS_MASK,POBJECT_ATTRIBUTES,PIO_STATUS_BLOCK,ULONG,ULONG,ULONG,PLARGE_INTEGER);
 NTSTATUS  WINAPI NtCreateMutant(HANDLE*,ACCESS_MASK,const OBJECT_ATTRIBUTES*,BOOLEAN);
 NTSTATUS  WINAPI NtCreateNamedPipeFile(PHANDLE,ULONG,POBJECT_ATTRIBUTES,PIO_STATUS_BLOCK,ULONG,ULONG,ULONG,ULONG,ULONG,ULONG,ULONG,ULONG,ULONG,PLARGE_INTEGER);
 NTSTATUS  WINAPI NtCreateSection(HANDLE*,ACCESS_MASK,const OBJECT_ATTRIBUTES*,const LARGE_INTEGER*,ULONG,ULONG,HANDLE);