freeradius3: fix hostname invocation in radtest

freeradius3: fix hostname invocation in radtest

Canonical radtest start results in an error:

$ radtest bob hello localhost 0 testing123
/usr/bin/radtest: line 1: hostname: not found
(0) Error parsing "stdin": Failed to get value

hostname command is not present in OpenWrt.
Instead, hostname can be obtained from file /proc/sys/kernel/hostname.

added: 004-get-hostname-from-proc-in-radtest.patch

Signed-off-by: Alexey Dobrovolsky <dobrovolskiy.alexey@gmail.com>