radvd: fix the radvd.service file to use /etc/sysconfig/radvd

This update fixes the following issue with radvd:
- bnc#854316: fix the radvd.service file to use /etc/sysconfig/radvd

Fixed bugs
bnc#854316
Typo in radvd.service: Unknown lvalue 'EnvironmentFile-' in section 'Service'
Selected Binaries
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