stdio-bridge: fix polled fds

Poll fds associated with the bus instead of hardcoding stdin/stdout.

This is consequential under socket activation, when the provided fd
should be used instead of stdin/stdout.

(cherry picked from commit 9d1c28b2d8422df700e7d94339ac6052a6755c6c)
(cherry picked from commit 59f5a4323468befbdca2bae7907219eaf8852f9a)
(cherry picked from commit a398d18e797d5b4dec6d265e753f8b688ffcd570)
(cherry picked from commit 0ae29e637c76a41d6e0ddf9f41d4c5e46b398d92)
(cherry picked from commit fb92304)
(cherry picked from commit eab1d97)

src/stdio-bridge/stdio-bridge.c

@@ -244,9 +244,9 @@ static int run(int argc, char *argv[]) {
                 t = usec_sub_unsigned(MIN(timeout_a, timeout_b), now(CLOCK_MONOTONIC));
 
                 struct pollfd p[3] = {
-                        { .fd = fd,            .events = events_a           },
-                        { .fd = STDIN_FILENO,  .events = events_b & POLLIN  },
-                        { .fd = STDOUT_FILENO, .events = events_b & POLLOUT },
+                        { .fd = fd,     .events = events_a           },
+                        { .fd = in_fd,  .events = events_b & POLLIN  },
+                        { .fd = out_fd, .events = events_b & POLLOUT },
                 };
 
                 r = ppoll_usec(p, ELEMENTSOF(p), t);