netutils/mdns: raise responder stack size default to 8KiB

CONFIG_NETUTILS_MDNS_STACKSIZE defaulted to DEFAULT_TASK_STACKSIZE,
which resolves to as little as 2KiB on some targets.  The bundled
mjansson responder uses a deeper stack than that (DNS record parsing
with name decompression, plus the send/receive buffers) and overflows
on startup, taking the board down with a hardfault before it answers a
single query.

Default to 8KiB, the value that reliably runs the responder, and
correct the help text, which previously claimed a 4KiB default that did
not match DEFAULT_TASK_STACKSIZE.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Ricard Rosson <ricard@groundbits.com>

Author: ricardgb

netutils/mdns/Kconfig

@@ -51,11 +51,15 @@ config NETUTILS_MDNS_PRIORITY
 
 config NETUTILS_MDNS_STACKSIZE
 	int "mDNS stack size"
-	default DEFAULT_TASK_STACKSIZE
+	default 8192
 	---help---
-		The default (4KiB) is adequate for simple networks but this will
-		most likely need to be increased if there are many network devices
-		attached that could send queries.
+		Stack size for the mDNS responder task.  The bundled mjansson
+		responder uses a fairly deep stack (record parsing with name
+		decompression plus the send/receive buffers), so the previous
+		default of DEFAULT_TASK_STACKSIZE overflows and hardfaults on
+		startup on targets where that resolves to a small value (e.g.
+		2KiB).  8KiB is adequate for typical networks; increase it further
+		if many devices on the network send queries.
 
 config NETUTILS_MDNS_VERBOSE
 	bool "Enable verbose printf output from built-in mdns demo"