mesh: Fix postponing storage deadline indefinitely
mesh: Fix postponing storage deadline indefinitely

If the local node keeps getting bombarded with messages, it's possible
that the storage timer gets rescheduled over and over again and never
expires. Add the necessary code to only reschedule the timer if the
new deadline is earlier than an existing one.

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