Forcing our routers just to accept connections from devices that we allow specifically, is a good practice to avoid MPLS Rogue Devices, from becoming neighbors in our network, thus, injecting bad information or capturing network sensitive data
You can control the information the routers sends using the mpls ldp discovery transport address and then select the correct IP Address that the router will use to open the TCP Session.
in this case R2 was configured
so if R2 changes the MPLS Router ID, we can assure that R2 in that interface will always attempt to establish a TCP session with R1 if R1 has a higher Router-ID
We can do the same configuration in R2, in order to prevent Rougue MPLS Devices