Dsmr: fix busy wait with ser2net

[andig]

Fix #8564

[vinc-vo]

Yes! Seems to work perfectly 👍

Still getting the errors when the connection is available (as expected), but with a decent amount of time in between.

openhabian@openHABianDevice:~/repo/evcc $ ./evcc
[main  ] INFO 2023/06/30 09:37:39 evcc 0.118.1 (b2b4483b)
[main  ] INFO 2023/06/30 09:37:39 using config file: /etc/evcc.yaml
[main  ] INFO 2023/06/30 09:37:39 starting ui and api at :7070
[db    ] INFO 2023/06/30 09:37:39 using sqlite database: /home/openhabian/.evcc/evcc.db
[dsmr  ] ERROR 2023/06/30 09:37:39 peek: EOF
[dsmr  ] ERROR 2023/06/30 09:37:39 peek: EOF
[dsmr  ] ERROR 2023/06/30 09:37:39 peek: EOF
[dsmr  ] ERROR 2023/06/30 09:37:39 peek: EOF
[dsmr  ] ERROR 2023/06/30 09:37:40 peek: EOF
[dsmr  ] ERROR 2023/06/30 09:37:42 peek: EOF
[dsmr  ] ERROR 2023/06/30 09:37:45 peek: EOF
[dsmr  ] ERROR 2023/06/30 09:37:53 peek: EOF
[main  ] FATAL 2023/06/30 09:37:54 cannot create meter 'grid1': cannot create meter 'template': cannot create meter 'dsmr': i/o timeout
[main  ] FATAL 2023/06/30 09:37:54 will attempt restart in: 5m0s
[dsmr  ] ERROR 2023/06/30 09:38:01 peek: EOF
[dsmr  ] ERROR 2023/06/30 09:38:16 peek: EOF
[main  ] FATAL 2023/06/30 09:38:17 evcc was stopped. OS should restart the service. Or restart manually.