GSoC 2017: patch for the stat/nanosecond bug

[Dmitry Savelyev]

Hello. My name is Dmitry Savelyev and I'm a third year student at CMC MSU
looking to participate in this year's GSoC with strace.

I have, of course, already submitted my proposal for netlink socket parsers,
although I did kind of screw it up in one part - namely I specified
NETLINK_ARPD as one of the netlink families for which to implement parsing.
Literally didn't realize it's gone from the kernel!

Anyway, here's my patch for (what I think is?) the stat/nanosecond printing
bug. I'm not sure about the signedness of the nanoseconds for statx though.