security: Trigger a ReadRemoteNameRequest on PinCodeRequest

The PinCodeRequest is the first event that we get
when we are in legacy pairing, and we need to have
the name before showing the UI prompt.

This was working before because RootCanal
incorrectly sent an IO Capability Exchange for
the initiator.

Test: gd/cert/run SecurityTest.test_successful_dut_initiated_pin
Change-Id: Ie8c7b6e3a49cd5c007d32c0b0d81058b1e70cdbf