RootCanal: Implement LL tests for LE periodic advertising

Added tests:
- LL/DDI/ADV/BV-26-C
- LL/DDI/SCN/BV-79-C

Fixed test:
- LL/DDI/ADV/BV-06-C
(broken after HCI disconnection code fixup patch)

Enabled test:
- LL/DDI/ADV/BV-20-C
(enabled by implementation of HCI LE Set Default Phy)

Bug: 275847929
Test: atest --host rootcanal_ll_test
Change-Id: Icde224c36b2b554dc3e28e521c716dc2eef617df