UsbAlsaManager: support MULTI_DEV_MULTI_CONN_MODE

Currently, only one active connection can be recognized in the
framework, and thus when multiple eligible devices exist, the new one
has to take place of the previous one.

This CL supports all such devices to be connected simultaneously,
without maintaining the "active connection" concept, behind the flag.

Bug: 367117623
Test: m
Flag: EXEMPT sysprop ro.audio.same_type_multi_device_allowed
Change-Id: I6798fe92757ed535a368bb4cb898e3a0886890da