libbinder: RPC more symmetrical max threads

Now, RpcServer and RpcSession both keep track of their max threads using
the same variable, and the server can therefore request the number of
reverse connections possible.

Bug: 185167543
Test: N/A
Change-Id: Ieaff69c8c2da2faf7598aed7e862601a1fcd7a00
5 files changed