ipv6: use ktime_t for internal timestamps

The ipv6 mip6 implementation is one of only a few users of the
skb_get_timestamp() function in the kernel, which is both unsafe
on 32-bit architectures because of the 2038 overflow, and slightly
less efficient than the skb_get_ktime() based approach.

This converts the function call and the mip6_report_rate_limiter
structure that stores the time stamp, eliminating all uses of
timeval in the ipv6 code.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>