Revert "Revert "Support socket activation of adb server""

Test: actually build both device and client adb this time

This reverts commit c77904e3c5b71e005e70ce0b1022501ac47b5677.

Change-Id: I8c2b8f24884ff36ff2460dab2500bad777100dfd
diff --git a/adb/client/commandline.cpp b/adb/client/commandline.cpp
index 0ffdbc2..6465ffe 100644
--- a/adb/client/commandline.cpp
+++ b/adb/client/commandline.cpp
@@ -107,6 +107,7 @@
         "       localfilesystem:<unix domain socket name>\n"
         "       dev:<character device name>\n"
         "       jdwp:<process pid> (remote only)\n"
+        "       acceptfd:<fd> (listen only)\n"
         " forward --remove LOCAL   remove specific forward socket connection\n"
         " forward --remove-all     remove all forward socket connections\n"
         " ppp TTY [PARAMETER...]   run PPP over USB\n"