[j-nsp] MX upgrade to 15.1R4.6: loopback filters drop all traffic

[Chuck Anderson]

Has anyone upgraded from 14.2 to 15.1 and seen this issue?  Right
after the upgrade, all loopback filters started dropping all traffic
causing OSPF & BGP failures, inability to ping or SSH into fxp0, etc.,
despite being configured to allow the appropriate management & control
plane traffic which was working perfectly fine in 14.2.
Deactivating/reactivating the filters "fixed" the issue, as did a full
box reboot.  Of course JTAC can't reproduce it.  64-bit Junos,
RE-1800X4's.