smb: enable reuse of deferred file handles for write operations

Previously, deferred file handles were reused only for read
operations, this commit extends to reusing deferred handles
for write operations. By reusing these handles we can reduce
the need for open/close operations over the wire.

Signed-off-by: Bharath SM <bharathsm@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>