nvmet-rdma: support max(16KB, PAGE_SIZE) inline data

The patch enables inline data sizes using up to 4 recv sges, and capping
the size at 16KB or at least 1 page size.  So on a 4K page system, up to
16KB is supported, and for a 64K page system 1 page of 64KB is supported.

We avoid > 0 order page allocations for the inline buffers by using
multiple recv sges, one for each page.  If the device cannot support
the configured inline data size due to lack of enough recv sges, then
log a warning and reduce the inline size.

Add a new configfs port attribute, called param_inline_data_size,
to allow configuring the size of inline data for a given nvmf port.
The maximum size allowed is still enforced by nvmet-rdma with
NVMET_RDMA_MAX_INLINE_DATA_SIZE, which is now max(16KB, PAGE_SIZE).
And the default size, if not specified via configfs, is still PAGE_SIZE.
This preserves the existing behavior, but allows larger inline sizes
for small page systems.  If the configured inline data size exceeds
NVMET_RDMA_MAX_INLINE_DATA_SIZE, a warning is logged and the size is
reduced.  If param_inline_data_size is set to 0, then inline data is
disabled for that nvmf port.

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>