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

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.

Reported by: bdrewery
Reviewed by: rmacklem
Tested by: pho
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D28306