selftests/net: psock_fanout: fix clang issues for target arch PowerPC

selftests/net: psock_fanout: fix clang issues for target arch PowerPC

Clang 9 threw:
warning: format specifies type 'unsigned short' but the argument has \
type 'int' [-Wformat]
                typeflags, PORT_BASE, PORT_BASE + port_off);

Tested: make -C tools/testing/selftests TARGETS="net" run_tests

Fixes: 77f65ebdca50 ("packet: packet fanout rollover during socket overload")
Signed-off-by: Tanner Love <tannerlove@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>