RootCanal: LE advertisement fixes

- Reject LE connection requests if advertising events
  are non-connectable (Core Specification v5.3,
  6.B § 4.4.2 Advertising state).

- Disable LE advertiser after LE connection request is received.

Test: cert/run
Change-Id: Id122ec8edd9a0fa15c0648862fe5d7055c73dcef