[PATCH usteer 1/2] build: use apk-compatible package date version

[AndreaCovelli]

Hi David,

Could you review the one-line APK date-version fix I sent on May 3?

https://patchwork.ozlabs.org/project/openwrt/patch/20260503231728.135249-1-andcov23@gmail.com/

The original patch still applies unchanged to
7532e1252fb937fe34b6da05e86fd34babd91ef5. The in-tree
openwrt/usteer/Makefile still uses --date=short.

I rechecked the version strings with the APK tool from the OpenWrt
25.12.5 SDK:

  apk version --check 2026-05-19-r1   # rejected, exit status 1
  apk version --check 2026.05.19-r1   # accepted, exit status 0

The patch switches the Git date format to %Y.%m.%d. This fixes builds
using usteer's in-tree OpenWrt Makefile; the normal packages feed already
converts PKG_SOURCE_DATE to a dotted version.

Could you merge this independently of the station policy exemption patch?

Thanks,
Andrea