socket-proxyd: Use ONESHOT to behave properly with multiple accept() processes.
bus: avoid 'bool' storage when retrieving 'b' from the message

Just use an unsigned int as a bool type to avoid issues in the public
message reading API; sizeof(bool) == 1, but the code copies 4 bytes at
the pointers destination.
socket-proxyd: Fix-up from previous change to avoid looping on errors.