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Support for IP_BIND_ADDRESS_NO_PORT sockopt was introduced in [1].
Recently [2] allowed its value to be accessed without locking the
socket.

Support for (newer) IP_LOCAL_PORT_RANGE sockopt was introduced in [3].
In the same series a selftest was added in [4]. This selftest also
covers the IP_BIND_ADDRESS_NO_PORT sockopt.

This patch enables getsockopt()/setsockopt() on MPTCP sockets for these
socket options, syncing set values to subflows in sync_socket_options().
Ephemeral port range is synced to subflows, enabling NAT usecase
described in [3].

[1] commit 90c337da ("inet: add IP_BIND_ADDRESS_NO_PORT to overcome
bind(0) limitations")
[2] commit ca571e2e ("inet: move inet->bind_address_no_port to
inet->inet_flags")
[3] commit 91d0b78c ("inet: Add IP_LOCAL_PORT_RANGE socket option")
[4] commit ae543965

 ("selftests/net: Cover the IP_LOCAL_PORT_RANGE
socket option")
Signed-off-by: Maxim Galaganov <max@internet.ru>
Revie...