nvmet: pass back cntlid on successful completion

According to the NVMe specification, the response dword 0 value of the
Connect command is based on status code: return cntlid for successful
compeltion return IPO and IATTR for connect invalid parameters.  Fix
a missing error information for a zero sized queue, and return the
cntlid also for I/O queue Connect commands.

Signed-off-by: Amit Engel <amit.engel@dell.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>