Fix adb leaking file descriptors to forked processes

accept() creates a new file descriptor that should be closed on exec so
that forked processes don't keep a fd opened on the socket.

This also fixes b/3297070 where adb hangs after running adb on the
target.

Change-Id: I8df511289e5549ae49b4824c9dfb71a3bf85eae8
diff --git a/adb/services.c b/adb/services.c
index 487c7d3..c22ce17 100644
--- a/adb/services.c
+++ b/adb/services.c
@@ -309,6 +309,7 @@
         dup2(pts, 1);
         dup2(pts, 2);
 
+        adb_close(pts);
         adb_close(ptm);
 
         execl(cmd, cmd, arg0, arg1, NULL);