[j-nsp] Upgrade to 15.1R4

[Jeff]

Hi,

we are using it on a MX240 with no major problems so far because of the 
NDP cache protection feature which was introduced with 15. We are seeing 
one at least annoying bug and that is that family inet6 configuration 
are sometimes not installed in the hardware. Removing and re-inserting 
them into the configuration does help as a work-around. I think we had 
that a couple of years ago already with Junos 10.x iirc as well.


Best,
Jeff