nfs client: block vnode_pager_setsize() calls from nfscl_loadattrcache in nfs_write

[kib]

Summary

Otherwise writing thread might wait on sbusy state of the pages which were busied by itself, similarly to nfs_read(). But also we need to clear NVNSETSZKSIP flag possibly set by ncl_pager_setsize(), to not undo extension done by write.

[pho]

I ran the 29 NFS tests I have with D28306.82766.diff. This was a 2 1/2 hour test.
No problems seen.

[rmacklem]

Looks fine to me, although I'll admit that I
do not really understand the vnode_pager_setsize()
stuff well enough to say whether or not this is correct?

[bdrewery]

Thanks!