rpc_binder: Change `trusty_tipc_fuzzer` to support multiple connections and messages

This changes `trusty_tipc_fuzzer` to be more like the existing binder rpc_fuzzer,
which opens and closes multiple connections and sends multiple messages in a single fuzz input.

The max number of connections is controlled by the define `TRUSTY_APP_MAX_CONNECTIONS`,
which defaults to `1`, thus keeping the existing behavior for now.

In the next CL, I'll add more fuzzers with `-DTRUSTY_APP_MAX_CONNECTIONS=10` instead.

Test: Build and run in trusty emulator
Change-Id: I9692e4d0295052a8da2204f63be9e52939e70ac3