RootCanal: Properly handle concurrent connection attempts

Previously, if two devices attempted to initiate a connection
simultaneously, two situations could occur:

- none of the attemps succeeds, as both have a local pending
  to the peer and the state does not allow for another pending
  connection

- one connection succeeds, but the other initiated connection
  ends with the HCI event Connect Complete (ERR_PAGE_TIMEOUT).
  This causes Android to disconnect the link afterwards.

This change adds an additional Page state to save the active
paging information. The pending connection state is reserved
for accepting remote connection requests.

Bug: 285597323
Test: atest --host rootcanal_ll_test
Change-Id: I24b469e73fbc02ed0525d712fbe4c1ac7390fb31