Improve handling of IPv6 routing type 0 extension headers.

- flow_weird event with name argument value of "routing0_hdr" is raised
  for packets containing an IPv6 routing type 0 header because this
  type of header is now deprecated according to RFC 5095.

- packets with a routing type 0 header and non-zero segments left
  now use the last address in that header in order to associate
  with a connection/flow and for calculating TCP/UDP checksums.

- added a set of IPv4/IPv6 TCP/UDP checksum unit tests

src/UDP.h

@@ -4,6 +4,7 @@
 #define udp_h
 
 #include "Analyzer.h"
+#include <netinet/udp.h>
 
 typedef enum {
 	UDP_INACTIVE,	// no packet seen
@@ -31,6 +32,10 @@ protected:
 	virtual bool IsReuse(double t, const u_char* pkt);
 	virtual unsigned int MemoryAllocation() const;
 
+	// Returns true if the checksum is valid, false if not
+	static bool ValidateChecksum(const IP_Hdr* ip, const struct udphdr* up,
+	                             int len);
+
 	bro_int_t request_len, reply_len;
 
 private: