I noticed that some people are trying to run mavros on the drone and are having problem with it, I myself included. I wanted to share some successes I had.
What I've noticed is that even after stopping mavlink-routerd, mavros will have problem connecting to /dev/ttyS1 outputting the error serial0: receive: End of file, as if the port is still in use.
Here is what I did that made it work eventually:
I disabled mavlink-routerd from startup by deleting S71mavlink-routerd from /etc/rc1.d through rc5.d ( I guess you can also modify or comment out the start() function in /etc/init.d/mavlink_routerd.sh)
Then after restarts, I can run roslaucnh mavros px4.launch fcu_url:=/dev/ttyS1:460800.
Note: 1 . this worked consistently for me after a power cycle, but the serial0:receive End of file error message should be gone instantly.
2. I haven't tried gcs reroute through mavros yet.