Push down td in the NFS server code.

[trasz]

Summary

Push down the thread argument in NFS server code, using curthread
instead of passing it explicitly. No functional changes. This is largely
a mechanical change, but I'd still prefer a second pair of eyes to make
sure I hadn't missed anything.

This includes changes from https://reviews.freebsd.org/D19417.
Obviously they will be committed separately.

[rmacklem]

Looks ok. I'm not sure I understand why having a lot of "struct thread *p = curthread;"s in
the local variables of the functions is an improvement over passing it as an argument,
but I see no harm in it?

[trasz]

The problem I'm trying to solve is that as it is right now, throughout the entire kernel, it's hard to say if you can call a kernel function for any thread, or just curthread. The way to fix it is to remove the thread argument in cases where it has to be equal to curthread.

I expect most of the newly added 'struct thread *p = curthread;' lines to disappear later on, when I push the 'td' even lower.

[trasz]

Regen.