Exclusion number in VANDERWAALS is ignored

The code to generate exclusions uses the nexcl value in the ELECTROSTATICS for both that and VANDERWAALS
```
auto myItype = InteractionType::ELECTROSTATICS;
if (!ffOption(*pd, myItype, "nexcl", &nexcl))
{
msghandler->fatal(gmx::formatString("The number of exclusions is not specified for %s in %s", interactionTypeToString(myItype).c_str(), pd->filename().c_str()));
}
auto exclusions = generateExclusions(msghandler, nexcl);
makePairs(msghandler, pd, InteractionType::VDW, exclusions);
makePairs(msghandler, pd, InteractionType::ELECTROSTATICS, exclusions);
```
so if the nexcl are different, the result would be incorrect.