client, server systemd units: make Restart=always truly respected (#184)

Surprisingly, Restart=always may not _always_ restart the unit if it restarts too fast.

Set a combination of options which should make systemd truly restart innernet always.
See https://unix.stackexchange.com/q/289629/352972.

The `RestartSec=60` is the main and important one which would prevent systemd from ever failing
to restart innernet in the default settings (because with it it would never exceed the default
limit of 5 restarts in 10 seconds).

`StartLimitIntervalSec=0` option is a complementary one for explicitly disabling the logic, and
may be removed from this PR if deemed unnecessary.

client/innernet@.service

@@ -8,6 +8,10 @@ PartOf=innernet.target
 Type=simple
 ExecStart=/usr/bin/innernet up %i --daemon --interval 60
 Restart=always
+# When the daemon exits, wait this amount of secs before restarting. Used to prevent StartLimitBurst
+# (5 by default) restarts happening within StartLimitIntervalSec (10 by default) after which systemd
+# would refrain from restarting innernet anymore.
+RestartSec=10
 
 [Install]
 WantedBy=multi-user.target

server/innernet-server@.service

@@ -8,6 +8,8 @@ Type=simple
 Environment="RUST_LOG=info"
 ExecStart=/usr/bin/innernet-server serve %i
 Restart=always
+# When the daemon exits, wait this amount of secs before restarting instead of default 100ms.
+RestartSec=1
 
 [Install]
 WantedBy=multi-user.target