Two patches in one:
1. Filter devices by USB VID:PID and USB bus device on Linux, in case you need to segregate devices onto different
   ADB dameons running on different server ports (like we needed several groups of Samsung phones, and they re-use
   their VID:PID for ALL devives):

ADB_DEV_BUS_USB=/dev/bus/usb/bus01 \
  ADB_VID_PID_FILTER=1234:8794,1344:2334 \
  ANDROID_ADB_SERVER_PORT=9123 adb devices

2. Bodge to grant unauthenticated access to adbd on a remote machine, and allow lots more emulators (we use this for 64 emulators):

Emulator host:
ADB_LOCAL_TRANSPORT_MAX=64 \
  ADB_LOCALHOST=name.of.this.hosting.machine.com \
  ./adb  start-server

Client host:
ADB_SERVER_SOCKET=tcp:name.of.hosting.machine.com:5037 ./adb devices

Note: the remote access is a bodge: run the patched adb on the emulator host, but the normal one elsewhere.