nfsd: use 64-bit seconds fields in nfsd v4 code

nfsd: use 64-bit seconds fields in nfsd v4 code

After commit 1295ea1c07c2 "vfs: change inode times to use struct
timespec64" there are spots in the NFSv4 decoding where we decode the
protocol into a struct timeval and then convert that into a timeval64.

That's unnecesary in the NFSv4 case since the on-the-wire protocol also
uses 64-bit values.  So just fix up our code to use timeval64 everywhere.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>