nvmf: Fix an off by one error when scanning active namespace IDs

[jhb]

Summary

The active namespace list query fetches namespaces greater than the
passed in namespace ID, not greater than or equal to the passed in
namespace ID. Thus, a multi-page request should start with the last
namespace ID from the previous page, not that ID plus 1.

While here, make use of NVME_GLOBAL_NAMESPACE_TAG instead of a magic
number to handle the edge case that the last namespace ID in a page is
the largest valid namespace ID.

Sponsored by: Chelsio Communications

[jhb]

Remove spurious nsid++