mptcp: add support for fullmesh flag

The link kernel supports this endpoint flag since v5.15, let's
expose it to user-space. It allows creation on fullmesh topolgy
via MPTCP subflow.

Additionally update the related man-page, clarifying the behavior
of related options.

Acked-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David Ahern <dsahern@kernel.org>
2 files changed