build: add urandom-seed and urngd to default packages set
urandom-seed content was split from base-files into separate package so
in order to preserve the current functionality and to provide some
fallback mechanism in case jent-rng initialization fails in urngd we
need to add it back.
urngd is OpenWrt's micro non-physical true random number generator based
on timing jitter.
Tested-by: Lucian Cristian <[email protected]>
Signed-off-by: Petr Štetiar <[email protected]>