ICMPv6: Add ICMPv6 Parameter Problem, code 3 definition

Based on RFC7112, Section 6:

   IANA has added the following "Type 4 - Parameter Problem" message to
   the "Internet Control Message Protocol version 6 (ICMPv6) Parameters"
   registry:

      CODE     NAME/DESCRIPTION
       3       IPv6 First Fragment has incomplete IPv6 Header Chain
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/uapi/linux/icmpv6.h

@@ -138,6 +138,7 @@ struct icmp6hdr {
 #define ICMPV6_HDR_FIELD		0
 #define ICMPV6_UNK_NEXTHDR		1
 #define ICMPV6_UNK_OPTION		2
+#define ICMPV6_HDR_INCOMP		3
 
 /*
  *	constants for (set|get)sockopt