Changes

testsuites: tunend: upf: Fix wrong format of some ip neigh commands

The ip-neigh+printf commands were taken from an older gtplab-sysmo2017
which was printing stuff as ".1%02u", but in the gtplab-sysmo2025
testsuite where they were put they were used to print ".%02u".

As a result, the following IP addresses where printed:
172.16.32.01
..
172.16.32.07
172.16.32.08
172.16.32.09
172.16.32.10

It turns out that commands such as ip neigh actually read integers
between dots as octal if they start with a leading 0.
As a result, addresses .01-.07 were working fine, since those octal
values match the decimal ones. However, .08 and .08 failed to be set due
to not being octal numbers.

As a result, when running eupf tunend ul+dl tests, DL traffic
encapsulated back aimed at RAN iface was, for some unknown reason, sent
over CN iface instead because it couldn't find an ARP resolution for it,
creating misbehaviors when running that testcase.

Change-Id: I1cdc9559aa8243c062d022f97a20ad8f8d3ad55b