Bluetooth: Only enable data length extensions when needed

We should disable the feature when it is not needed to
save flash and RAM.
There is no point in enabling data length extensions
when the maximum packet size used is always smaller or equal
to 27 bytes. Then data length updates would only use
parameters (octets=27, time=T) where T is some supported value
which would not improve throughput or power consumption.

Signed-off-by: Rubin Gerritsen <[email protected]>

Author: rugeGerritsen

subsys/bluetooth/Kconfig

@@ -147,7 +147,7 @@ config BT_PHY_UPDATE
 
 config BT_DATA_LEN_UPDATE
 	bool "Data Length Update"
-	default y
+	default y if ((BT_BUF_ACL_TX_SIZE > 27) || (BT_BUF_ACL_RX_SIZE > 27))
 	depends on !BT_CTLR || BT_CTLR_DATA_LEN_UPDATE_SUPPORT
 	help
 	  Enable support for Bluetooth v4.2 LE Data Length Update procedure.