rps: Inspect PPTP encapsulated by GRE to get flow hash

The PPTP is encapsulated by GRE header with that GRE_VERSION bits
must contain one. But current GRE RPS needs the GRE_VERSION must be
zero. So RPS does not work for PPTP traffic.

In my test environment, there are four MIPS cores, and all traffic
are passed through by PPTP. As a result, only one core is 100% busy
while other three cores are very idle. After this patch, the usage
of four cores are balanced well.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
Reviewed-by: Philip Prindeville <philipp@redfish-solutions.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ppp/pptp.c b/drivers/net/ppp/pptp.c
index ae0905e..3e68dbc 100644
--- a/drivers/net/ppp/pptp.c
+++ b/drivers/net/ppp/pptp.c
@@ -37,6 +37,7 @@
 #include <net/icmp.h>
 #include <net/route.h>
 #include <net/gre.h>
+#include <net/pptp.h>
 
 #include <linux/uaccess.h>
 
@@ -53,41 +54,6 @@
 static const struct ppp_channel_ops pptp_chan_ops;
 static const struct proto_ops pptp_ops;
 
-#define PPP_LCP_ECHOREQ 0x09
-#define PPP_LCP_ECHOREP 0x0A
-#define SC_RCV_BITS	(SC_RCV_B7_1|SC_RCV_B7_0|SC_RCV_ODDP|SC_RCV_EVNP)
-
-#define MISSING_WINDOW 20
-#define WRAPPED(curseq, lastseq)\
-	((((curseq) & 0xffffff00) == 0) &&\
-	(((lastseq) & 0xffffff00) == 0xffffff00))
-
-#define PPTP_GRE_PROTO  0x880B
-#define PPTP_GRE_VER    0x1
-
-#define PPTP_GRE_FLAG_C	0x80
-#define PPTP_GRE_FLAG_R	0x40
-#define PPTP_GRE_FLAG_K	0x20
-#define PPTP_GRE_FLAG_S	0x10
-#define PPTP_GRE_FLAG_A	0x80
-
-#define PPTP_GRE_IS_C(f) ((f)&PPTP_GRE_FLAG_C)
-#define PPTP_GRE_IS_R(f) ((f)&PPTP_GRE_FLAG_R)
-#define PPTP_GRE_IS_K(f) ((f)&PPTP_GRE_FLAG_K)
-#define PPTP_GRE_IS_S(f) ((f)&PPTP_GRE_FLAG_S)
-#define PPTP_GRE_IS_A(f) ((f)&PPTP_GRE_FLAG_A)
-
-#define PPTP_HEADER_OVERHEAD (2+sizeof(struct pptp_gre_header))
-struct pptp_gre_header {
-	u8  flags;
-	u8  ver;
-	__be16 protocol;
-	__be16 payload_len;
-	__be16 call_id;
-	__be32 seq;
-	__be32 ack;
-} __packed;
-
 static struct pppox_sock *lookup_chan(u16 call_id, __be32 s_addr)
 {
 	struct pppox_sock *sock;