Drivers: MPSL: Reduce flash radio sync timeout for Mesh use cases

After changes in how MPSL uses the
CONFIG_SOC_FLASH_NRF_RADIO_SYNC_MPSL_NORMAL_PRIORITY_TIMEOUT_US value,
Mesh applications started observing some slowdown in roundtrip
point-to-point message and response. This is because Mesh now needs to
wait for the entire timeout as part of a roundtrip. Decreasing the
timeout to 5ms moves us close to where we were before the recent
changes to MPSL, without over-prioritizing flash timeslots.

Signed-off-by: Ludvig Jordet <[email protected]>

Author: ludvigsj

drivers/mpsl/flash_sync/Kconfig

@@ -42,6 +42,7 @@ config SOC_FLASH_NRF_RADIO_SYNC_MPSL_NORMAL_PRIORITY_TIMEOUT_US
 	int "Timeout for normal priority MPSL request [us]"
 	depends on SOC_FLASH_NRF_RADIO_SYNC_MPSL
 	range 0 1000000
+	default 5000 if BT_MESH
 	default 10000
 	help
 	  The flash synchronization mechanism relies on MPSL timeslots.