[trustthegoose]

Part 1 of deepsealabs/libdc-swift#78, split out as requested because it affects stock build 22.

Problem

When the Suunto app is connected on the same phone, it holds subscriptions of its own, and the watch pushes their values over the shared link as 0x01 notifications with sequence number 0, the same opcode and sequence number as our /Data stream chunks. suunto_nautic_stream() takes every such packet as a chunk, so one of them fails the stream:

20:37:17.793 suunto_nautic_stream(): Unexpected chunk size (10).
20:37:18.120 suunto_nautic_download(): Retrying the stream of dive 1789487761.
20:37:22.895 suunto_nautic_stream(): Unexpected chunk size (10).

Both were the same notification, on another handle (Nautic, DC Tester build 22 on an iPad with the Suunto app connected):

A5 01 0A 00 | 00 00 | F0 BF 06 | 01 80 00 | 01 00 00 00 | crc

The watch also pushes that value to the app every 30 minutes, so the stray packet can turn up during any long download while the Suunto app is connected.

Fix

Skip a notification whose handle isn't the stream's. One wrinkle: compare the handle without its slot byte. Our stream's chunks carry the handle with slot F0, while the GET reply that bound it has slot 00 (e.g. chunks F0 24 0E for GET 00 24 0E); a full three-byte compare rejects every chunk of our own stream. The other subscription differs in the remaining two bytes (BF 06 vs 24 0E).

Testing

• Compiles without warnings (-Wall -Wextra), same as the base.
• On hardware, this check is part of the full pause-and-resume set from Nautic/Ocean: let downloads coexist with the Suunto app on the same phone (pause and resume instead of truncating) libdc-swift#78: with it, a 12-entry Nautic download with the Suunto app connected and three forced takeovers finished with every entry at its listed size: the new check skipped 8 such notifications, and there were no "Unexpected chunk size" failures (the run before it had two). Without the rest of Nautic/Ocean: let downloads coexist with the Suunto app on the same phone (pause and resume instead of truncating) libdc-swift#78 I can't easily stage a clean run of this change alone, since what makes the Suunto app's subscriptions push mid-download (it reconnecting) also cuts the stream; that part is the second PR.