Fix RADIUS error reporting in hba file parsing

The RADIUS-related checks in parse_hba_line() did not respect elevel
and did not fill in *err_msg. Also, verify_option_list_length()
pasted together error messages in an untranslatable way. To fix the
latter, remove the function and do the error checking inline. It's a
bit more verbose but only minimally longer, and it makes fixing the
first two issues straightforward.