mptcp: add some missing pr_fmt defines

Some of the mptcp logs didn't print out the format string:

[  185.651493] DSS
[  185.651494] data_fin=0 dsn64=0 use_map=0 ack64=1 use_ack=1
[  185.651494] data_ack=13792750332298763796
[  185.651495] MPTCP: msk=00000000c4b81cfc ssk=000000009743af53 data_avail=0 skb=0000000063dc595d
[  185.651495] MPTCP: msk=00000000c4b81cfc ssk=000000009743af53 status=0
[  185.651495] MPTCP: msk ack_seq=9bbc894565aa2f9a subflow ack_seq=9bbc894565aa2f9a
[  185.651496] MPTCP: msk=00000000c4b81cfc ssk=000000009743af53 data_avail=1 skb=0000000012e809e1

So this patch added these missing pr_fmt defines. Then we can get the same
format string "MPTCP" in all mptcp logs like this:

[  142.795829] MPTCP: DSS
[  142.795829] MPTCP: data_fin=0 dsn64=0 use_map=0 ack64=1 use_ack=1
[  142.795829] MPTCP: data_ack=8089704603109242421
[  142.795830] MPTCP: msk=00000000133a24e0 ssk=000000002e508c64 data_avail=0 skb=00000000d5f230df
[  142.795830] MPTCP: msk=00000000133a24e0 ssk=000000002e508c64 status=0
[  142.795831] MPTCP: msk ack_seq=66790290f1199d9b subflow ack_seq=66790290f1199d9b
[  142.795831] MPTCP: msk=00000000133a24e0 ssk=000000002e508c64 data_avail=1 skb=00000000de5aca2e
Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/options.c

@@ -4,6 +4,8 @@
  * Copyright (c) 2017 - 2019, Intel Corporation.
  */
 
+#define pr_fmt(fmt) "MPTCP: " fmt
+
 #include <linux/kernel.h>
 #include <net/tcp.h>
 #include <net/mptcp.h>

net/mptcp/pm.c

@@ -3,6 +3,8 @@
  *
  * Copyright (c) 2019, Intel Corporation.
  */
+#define pr_fmt(fmt) "MPTCP: " fmt
+
 #include <linux/kernel.h>
 #include <net/tcp.h>
 #include <net/mptcp.h>

net/mptcp/pm_netlink.c

@@ -4,6 +4,8 @@
  * Copyright (c) 2020, Red Hat, Inc.
  */
 
+#define pr_fmt(fmt) "MPTCP: " fmt
+
 #include <linux/inet.h>
 #include <linux/kernel.h>
 #include <net/tcp.h>