(Sandbox) Unexpected syscalls on relay

weasel reported the following sandxbox warnings on his relay:

(Sandbox) Caught a bad syscall attempt (syscall eventfd2)
/usr/bin/tor(+0x1328b6)[0x7f71180d18b6]
/lib/x86_64-linux-gnu/libc.so.6(eventfd+0xd)[0x7f711649e2fd]
/lib/x86_64-linux-gnu/libc.so.6(eventfd+0xd)[0x7f711649e2fd]
/usr/bin/tor(alert_sockets_create+0xec)[0x7f71180bef9c]

 (Sandbox) Caught a bad syscall attempt (syscall open)
 /usr/bin/tor(+0x1328b6)[0x7f653db158b6]
 /lib/x86_64-linux-gnu/libpthread.so.0(open64+0x10)[0x7f653c3b81d0]
 /lib/x86_64-linux-gnu/libpthread.so.0(open64+0x10)[0x7f653c3b81d0]
 /usr/bin/tor(tor_open_cloexec+0x40)[0x7f653daff5e0]
 /usr/bin/tor(start_writing_to_file+0xf2)[0x7f653db10732]
 /usr/bin/tor(+0x12d89b)[0x7f653db1089b]
 /usr/bin/tor(+0x12d9e8)[0x7f653db109e8]
 /usr/bin/tor(crypto_pk_write_private_key_to_filename+0xcb)[0x7f653db1f57b]

We should probably test the sandbox more thoroughly on relay-mode. Here is the torrc used (to reproduce this):

Sandbox 1
PublishServerDescriptor 0
OrPort 9031