With recent changes in the VCL state and temperature handling this test
case lost its relevance and started testing a no-op operation. And since
it wasn't apparently obvious what it was trying to check between two
possible interpretations it now tests both and better verifies it.

Reported by fgs.

When I initially wrote this test case it used to trigger a panic in the
then young VCL labeling.

If an absolute path is provided as n_arg with a length of exactly
PATH_MAX-1 then the combination of strcpy and strcat for the trailing
slash '/' overflows dn by one byte, writing its new null-terminating
character '\0' right after dn's upper bound.

By using a fixed-length VSB we can simply ensure that we stay within
bounds at a reasonable cost. Guarding VSB operations should silence
Flexelint as a nice side effect.

VIN_n_Arg is not exposed outside of the source tree, and both callers
today provide a valid dir argument, so we can now make it part of the
contract with an assertion, simplifying the strdup error handling.

cold&discard for their VCL.

Closes: #2471

we want a single unique suckaddr.

When an object is dying, we would rather not have the ban
lurker evalueate it against any existing bans. Now it will,
when a dying object is found, simply remove the oc off the
ban list completely. This is very cheap since we are already
holding the oh and ban mutexes.

This reverts commit f9c9db4a.

Relevant to #2800

The former fails in some platforms but we can test the latter.

It currently freaks out when it's not aware of a type, or when it
encounters v_*_ macros in a function signature. This doesn't improve the
results of the existing patches but we should take a habit of specifying
where additional C includes are.