Add -yy option: print ip and port associated with socket descriptors

Add -yy option: print ip and port associated with socket descriptors

When two ore more -y options are given, print local and remote ip:port
pairs associated with socket descriptors.  This implementation uses
NETLINK_INET_DIAG for sockaddr lookup; it's based on the patch
prepared by Zubin Mithra as a part of his GSoC 2014 strace project.

* Makefile.am (strace_SOURCES): Add socketutils.c
(EXTRA_DIST): Add linux/inet_diag.h and linux/sock_diag.h.
* defs.h (print_sockaddr_by_inode): New prototype.
* linux/inet_diag.h: New file.
* linux/sock_diag.h: Likewise.
* socketutils.c: Likewise.
* strace.1: Document -yy option.
* strace.c (usage): Likewise.
* util.c (printfd): Use print_sockaddr_by_inode.