patch/Support-for-fullcone-nat: Add git mbox patch header back

The format created by `git format-patch` allows to easily apply the
patch to the Linux source with `git am`, simplying development and
upstreaming.

Note, the header was removed when forward porting the patch to a newer
Linux kernel version.

Fixes: c6aeedd ("Updated NAT kernel patch for 4.19 buster (sonic-net#147)")
Cc: Akhilesh Samineni <akhilesh.samineni@broadcom.com>

patch/Support-for-fullcone-nat.patch

@@ -1,3 +1,25 @@
+From 67cc2bd46c7ad1431ddd1819cdfad6ecc08a7593 Mon Sep 17 00:00:00 2001
+From: Kiran Kella <kiran.kella@broadcom.com>
+Date: Fri, 6 Sep 2019 20:54:19 -0700
+Subject: [PATCH] Support for fullcone nat
+
+---
+ include/net/netfilter/nf_conntrack.h     |   3 +
+ include/net/netfilter/nf_nat.h           |   6 +
+ include/net/netfilter/nf_nat_l4proto.h   |  12 +-
+ include/uapi/linux/netfilter/nf_nat.h    |   1 +
+ net/ipv4/netfilter/nf_nat_proto_gre.c    |   8 +-
+ net/ipv4/netfilter/nf_nat_proto_icmp.c   |   6 +-
+ net/ipv6/netfilter/nf_nat_proto_icmpv6.c |   5 +-
+ net/netfilter/nf_nat_core.c              | 173 ++++++++++++++++++++---
+ net/netfilter/nf_nat_proto_common.c      |  32 +++--
+ net/netfilter/nf_nat_proto_dccp.c        |   6 +-
+ net/netfilter/nf_nat_proto_sctp.c        |   6 +-
+ net/netfilter/nf_nat_proto_tcp.c         |   6 +-
+ net/netfilter/nf_nat_proto_udp.c         |  12 +-
+ net/netfilter/nf_nat_proto_unknown.c     |   4 +-
+ 14 files changed, 220 insertions(+), 60 deletions(-)
+
 diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
 index f45141bdbb83..64b9293a31f6 100644
 --- a/include/net/netfilter/nf_conntrack.h