Changes

examples/*.config: change diameter_ip to 127.0.0.8

Change the default diameter_ip from 127.0.0.4 to 127.0.0.8. This is the
IP that open5gs MME expects the HSS to be running at, so it will work
out of the box. With 127.0.0.4 we get a conflict with the SMF.

The default has already been changed like this in 9ff2e8 ("diameter:
Change default bind IP to 127.0.0.8"). But only for the case when
running without a config - in the default config it was still set to
127.0.0.4.

Related: SYS#7413
Related: https://github.com/open5gs/open5gs/blob/787e55550183a661943d84ab67239c92f0be698c/configs/freeDiameter/mme.conf.in#L264
Change-Id: I252f96a3e8ead8fbf1715b14746b227e9edc62c9