Mk/bsd.sites.mk: Update MASTER_SITE_DEBIAN

1. cdn.debian.net and http.debian.net are obsolete, so replace them with deb.debian.org.
2. Sync per-country mirrors with current official mirrors list.

Reference: https://www.debian.org/mirror/list (1,2)
Reference: https://wiki.debian.org/DebianGeoMirror (1)