zpool wait: print timestamp before the header

[robn]

Motivation and Context

zpool list, status and iostat all display the -T timestamp before the header, but wait showed it after. Make it be like the others.

Description

Just moves the print up.

How Has This Been Tested?

By hand. Before:

$ ./zpool wait -T u lucy 1
  DISCARD    FREE  INITIALIZE  REPLACE  REMOVE  RESILVER   SCRUB    TRIM  RAIDZ_EXPAND
1706247328
        0       0           0        0       0         0       0       0             0

after:

$ ./zpool wait -T u lucy 1
1706247336
  DISCARD    FREE  INITIALIZE  REPLACE  REMOVE  RESILVER   SCRUB    TRIM  RAIDZ_EXPAND
        0       0           0        0       0         0       0       0             0

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[behlendorf]

Thanks!