[PATCH] df: correct BLOCKSIZE handling for -k to use 1K-blocks (290710)

From: Ankush Mondal <ankushmondal1y2t_at_gmail.com>
Date: Mon, 24 Nov 2025 13:04:20 UTC
This patch fixes the inconsistency in df -k header formatting described in Bug
290710 <https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=290710#c0>.

Before :
root@bsd:~ # df -k
Filesystem           1024-blocks         Used     Avail Capacity  Mounted on
zroot/ROOT/default    65618056     4716712   60901344     7%      /

After :
root@bsd:~ # df -k
Filesystem           1K-blocks         Used     Avail Capacity  Mounted on
zroot/ROOT/default    65618056     4716712   60901344     7%      /