Fix the NFSv4 client so that it checks for support of TimeCreate before
trying to set it.

r362490 added support for setting of the TimeCreate (va_birthtime) attribute,
but it does so without checking to see if the server supports the attribute.
This could result in NFSERR_ATTRNOTSUPP error replies to the Setattr operation.
This patch adds code to check that the server supports TimeCreate before
attempting to do a Setattr of it to avoid these error returns.