selftests: Fix suppress test in fib_tests.sh

fib_tests is spewing errors:
    ...
    Cannot open network namespace "ns1": No such file or directory
    Cannot open network namespace "ns1": No such file or directory
    Cannot open network namespace "ns1": No such file or directory
    Cannot open network namespace "ns1": No such file or directory
    ping: connect: Network is unreachable
    Cannot open network namespace "ns1": No such file or directory
    Cannot open network namespace "ns1": No such file or directory
    ...

Each test entry in fib_tests is supposed to do its own setup and
cleanup. Right now the $IP commands in fib_suppress_test are
failing because there is no ns1. Add the setup/cleanup and logging
expected for each test.

Fixes: ca7a03c4

 ("ipv6: do not free rt if FIB_LOOKUP_NOREF is set on suppress rule")
Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>