nack pli about jicofo

[gpolitis]

FF doesn't care about what we include in the offer, it sends PLIs. Tested with FF 37, 38, 39. We should probably add this line. I think Chrome behaves correctly though, i.e. it doesn't send PLIs when they're not signaled, it relies on NACKs. Issue 2252 enables this line for Chrome 34.

[gpolitis]

@bgrozev this could potentially affect NACK termination if, by enabling this line, Chrome favors PLI instead of NACKs. In theory, they're two different things and shouldn't clash but I'm pinging you just in case this breaks something in practice.

[fippo]

i've been using it for months and not seen anything that breaks

[paweldomas]

Thanks ! Included in c7af700