haveged: small improvements

Source of the changes:
https://github.com/freifunk-gluon/gluon/blob/master/patches/packages/openwrt/0001-haveged-start-directly-after-initial-setup-and-disable-tests.patch

"haveged: start earlier in boot sequence"
This way, crypto based programs that run on startup can make use of the additional entropy provided by haveged.

"haveged: disable online testing"
From the haveged README:
"The --enable-olt option is provided to suppress the entire online test facility.
This option is provided for systems with a very limited resource budget and the
ability to thoroughly test the RNG output by other means. When enabled, the online
test system tests the output of the haveged random number generator using AIS-31
test procedures A and B. Either or both tests may be run as a total failure check
(a "tot" test) at initialization and/or continuously during all subsequent haveged
operation - See the man page and the description at
http://www.issihosts.com/haveged/ais31.html for further information."

It seems to be usefull to apply these changes to the official OpenWrt package.