Account for new entry becoming pending
Account for new entry becoming pending

Summary:
A entry can transition from being resolved to pending
when either
a) The corresponding port goes down
b) In the course of expiring entries

We must correctly program these to drop, since that's what pending
entry corresponds to in the s/w state.

Reviewed By: aeckert

Differential Revision: D2607905

fb-gh-sync-id: ab1a1419cbfe7a66b2bdcaa2aa9b2da0b82fe861

peterlei/fboss,neuhausler/fboss,peterlei/fboss,neuhausler/fboss,peterlei/fboss,neuhausler/fboss,peterlei/fboss,neuhausler/fboss