smb3: request more credits on normal (non-large read/write) ops

We can end up building up credits too slowly to do large operations
(reads and writes for example) that require many credits. By
comparison most other SMB3 clients request many more (sometimes
thousands) of credits on all operations.  Increase
the number of credits we request on typical (non-large e.g
read/write) operations to 10 from 2 so we can build a pool of credits
faster.

Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>