With a mortgage of €280k, you are paying around €3,000 interest a year at present.
Most of your monthly repayment is going in capital repayments, so even without movements in the value of the property, you will eliminate the negative equity fairly quickly.
There is a fair chance that the rent restrictions won't be renewed when they expire, so the rent shortfall may be only temporary.
Investors won't buy your property because of the rent restriction, so the price might be artificially low.
All in all, you should wait a while before selling.
Brendan