ui: make interactive and non-interactive exit code the same

ui: make interactive and non-interactive exit code the same

Before this change the report gave successful exit value when destination
hostname could not be found.

    $ ./mtr --report nxdomain. ; echo $?
    ./mtr: Failed to resolve host: nxdomain.: Name or service not known
    0

Quickly looking 'git grep ---after-context if.*Interactive' there does not
appear to be more than the two instances in main() where exit is called
depending on interactive, so this change should cover all these cases.

Reported-by: Marek Kroemeke <mkroemeke@cloudflare.com>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>