t/io_uring: Reporting bandwidth

t/io_uring: Reporting bandwidth

When performing tests at various block size, it's sometimes a bit
difficult to estimate if we reach the limit of the datapath.

This commit offer to simply prints the resulting bandwitdh of the IOPS
multiplied by the block size.

A typical output looks like :

  [user@hosŧ] t/io_uring -b512 -d128 -c32 -s32 -p1 -F1 -B1 -n4 /dev/nvme0n1
   ...
   IOPS=729856, BW=356 MiB/s, IOS/call=32/32, inflight=(105 119 108 109)

  [user@host] t/io_uring -b4096 -d128 -c32 -s32 -p1 -F1 -B1 -n4 /dev/nvme0n1
   ...
   IOPS=746368, BW=2915 MiB/s, IOS/call=32/31, inflight=(121 115 122 122)

In the 4K case, as for a PCI Gen3 product, we are clearly limited by the
bandwidth while in the 512 case we hit latency issues.

BW is expressed in MiB/sec.

Signed-off-by: Erwan Velu <e.velu@criteo.com>