host/mesh: proxy: update delayable work
host/mesh: proxy: update delayable work

Switch to the new API. Adds check for a pending buffer in the SAR
timeout handler.

This is port of 1577fec8511d18778e39e0edb952cf468ff0735c

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble