rate_ctr: don't use . as separator

Use ':' as separator, so that no mangled rate_ctr descriptions are allocated.

When '.' is used, the rate_ctr mangling code creates tallocs of mangled counter
descriptors, and hence affects the amount of expected talloc contexts in
msc_vlr_tests.c.

Change-Id: Ib1db8e3dc6c833174f1b0b1ca051b0861f477408
1 file changed