MAINTAINERS: add git trees for MPTCP

This will help occasional developers to find our git repo without having
to look at our wiki.
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -14617,6 +14617,8 @@ L:	mptcp@lists.linux.dev
 S:	Maintained
 W:	https://github.com/multipath-tcp/mptcp_net-next/wiki
 B:	https://github.com/multipath-tcp/mptcp_net-next/issues
+T:	git https://github.com/multipath-tcp/mptcp_net-next.git export-net
+T:	git https://github.com/multipath-tcp/mptcp_net-next.git export
 F:	Documentation/networking/mptcp-sysctl.rst
 F:	include/net/mptcp.h
 F:	include/trace/events/mptcp.h