Do not obtain and hold a mbuf just to transmit advertisements.
Do not obtain and hold a mbuf just to transmit advertisements.

The code prior to this change would grab a mbuf and hold it
forever (in the state machine) so that it could transmit
advertisements. The new code just attempts to allocate a mbuf
to transmit. If it cannot, that advertisement just doesnt
get sent.

X-Original-Commit: bfb7f447ed62756219598e00cb278d1e883e1163

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