Add header to vendor commands in effects-log

Add header to vendor commands in effects-log

This patch adds a header preceding the opcode list when printing the
effects-log:

nvme effects-log /dev/nvmex
Admin Commands
ACS0     [Delete I/O Submission Queue     ] 00000001
ACS1     [Create I/O Submission Queue     ] 00000001
<snip>

Vendor Specific Admin Commands
ACS198   [Unknown                         ] 00000001
ACS204   [Unknown                         ] 0002001f

I/O Commands
IOCS0    [Flush                           ] 00000001
IOCS1    [Write                           ] 00000003
<snip>

Vendor Specific I/O Commands
IOCS129  [Unknown                         ] 00000003

The patch does not change binary or json output formats.

Signed-off-by: Andreas Hindborg <andreas.hindborg@wdc.com>