By default systemd kills the service which causes an OOM. That make
sense for a typical service, however, for SSH we don't want this
behavior: The connection should continue, just the command which caused
OOM should be killed.
So far the exit code has been evaluated, which seems to be non-zero even
with a regular term signal. With that systemd assumed the service is in
a failed state, when in fact this seems the regular behavior of dropbear
when shutting it down.
