selftests: icmp_redirect: pass xfail=0 to log_test()

If any sub-test in this icmp_redirect.sh is failing but not expected
to fail. The script will complain:
    ./icmp_redirect.sh: line 72: [: 1: unary operator expected

This is because when the sub-test is not expected to fail, we won't
pass any value for the xfail local variable in log_test() and thus
it's empty. Fix this by passing 0 as the 4th variable to log_test()
for non-xfail cases.

v2: added fixes tag

Fixes: 0a36a75c ("selftests: icmp_redirect: support expected failures")
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>