fix(icom): decode the network RX audio as what the rig actually sends

The first real radio on the 50003 stream (an IC-7760) settles the two guesses
the experimental audio path shipped with. The payload starts at 0x18 — the
packet carries a big-endian payload length at 0x14 (0x500 on every packet) —
not at 0x16, which swallowed two header bytes into the PCM and laid a 50 Hz
click track under everything. And rxcodec 0x10 asks for TWO-channel LPCM,
which the mono playback path rendered as double-speed garble; 0x02 asks for
the one channel the monitor plays.

changelog.json

@@ -6,13 +6,15 @@
       "Elecraft console: the S-meter is calibrated against a real K3 — S9 and the +dB readings now match the radio’s own display (they read about two S-units low).",
       "Elecraft console: an SWR spike (the K3’s own blip at the end of an FT8 frame) no longer fades over twelve seconds — the peak shows briefly, then the meter returns straight to the live reading.",
       "Icom: the IC-7760 joins the model list (CI-V address B2h).",
-      "Icom console: the IC-7760 gets its real attenuator steps — 6/12/18 dB."
+      "Icom console: the IC-7760 gets its real attenuator steps — 6/12/18 dB.",
+      "Icom network audio: the RX stream is decoded correctly — mono is requested and the payload offset was confirmed on a real IC-7760, curing the garbled, clicking audio."
     ],
     "fr": [
       "Console Elecraft : le S-mètre est calibré sur un vrai K3 — S9 et les +dB correspondent désormais à l’affichage de la radio (il lisait environ deux points S trop bas).",
       "Console Elecraft : un pic de ROS (le sursaut du K3 en fin de trame FT8) ne s’estompe plus pendant douze secondes — le pic s’affiche brièvement, puis le ros-mètre revient directement à la valeur réelle.",
       "Icom : l’IC-7760 rejoint la liste des modèles (adresse CI-V B2h).",
-      "Console Icom : l’IC-7760 reçoit ses vrais crans d’atténuateur — 6/12/18 dB."
+      "Console Icom : l’IC-7760 reçoit ses vrais crans d’atténuateur — 6/12/18 dB.",
+      "Audio réseau Icom : le flux RX est décodé correctement — le mono est demandé et l’offset du payload a été confirmé sur un vrai IC-7760, ce qui guérit le son inaudible et les clics."
     ]
   },
   {