Compile fixes for OpenBSD, and call freeaddrinfo() in rtp.c

Added compile fixes for OpenBSD:
* add #includes like <netinet/in.h>, so IPV6_V6ONLY, IPPROTO_TCP, and others get defined
* define AI_ADDRCONFIG (which is not supported on OpenBSD/NetBSD)

Also, call freeaddrinfo() in rtp.c, to free the memory allocated by getaddrinfo()

1.0-dev is working for me on OpenBSD 5.2/i386