ltp-networking/tcp_cmds/finger: fix finger test

Ubuntu use modified finger command. finger an unknown host test will
return nonzero on Ubuntu 12.04 even if successful execution.

for example:
on Ubuntu
    finger @xxx 2>&1 1>/dev/null ; echo $?
will return
    finger: unknown host: xxx
    getaddrinfo: No address associated with hostname
    1
on CentOS
    finger @xxx 2>&1 1>/dev/null ; echo $?
will return
    finger: xxx: nodename nor servname provided, or not known
    0

Signed-off-by: Vincent Hsu <vincent.hsu@linaro.org>
ltp-networking/iproute: fix iproute test

ip02: set original mtu size back. this test will modify mtu to 300.
ip05: if there is not only one route, using "head" command will get
      wrong result.

Signed-off-by: Vincent Hsu <vincent.hsu@linaro.org>