currentMtu

Returns the current ATT MTU.

This method is called when the peripheral is connected to feed mtu flow.

The default implementation derives the MTU from maximumWriteValueLength, which is how it is available when the system negotiates it. As the write length is capped at 512 bytes, the result is exact only below 515; for greater MTUs it is the lower bound. Platforms that know the exact value should override this method.