nimble/ll: Fix not clearing scan rsp on scan duration timeout
nimble/ll: Fix not clearing scan rsp on scan duration timeout

If timeout fired when we were waiting for scan response,
scan_rsp_pending would be left set and this would trigger assert
when starting next scan.

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