selftests/net: add MPTCP coverage for IP_LOCAL_PORT_RANGE

Since previous commit, MPTCP has support for IP_BIND_ADDRESS_NO_PORT and
IP_LOCAL_PORT_RANGE sockopts.

Add ip4_mptcp and ip6_mptcp fixture variants to ip_local_port_range
selftest to provide selftest coverage for these sockopts.

Acked-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Maxim Galaganov <max@internet.ru>
Signed-off-by: Matthieu Baerts <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>