Use correct size for VLAN tag load instruction

[dmiller-nmap]

Not a true bug, since Linux kernel (net/core/filter.c) forces any load from SKF_AD_VLAN_TAG to a BPF_H width. However, this change makes libpcap code easier to understand.

[infrastation]

One CI worker failed due to timeouts on a busy host, another failed due to a macOS issue that should disappear after rebasing on the current master branch.

[dmiller-nmap]

The only failed check appears to be a timeout: valid_wlan_subtype_qos_cf_poll_opt (alias 2): failed (filtertest timeout)

Any comments on this change?

[guyharris]

Any comments on this change?

None on my part; as Denis noted, the timeout was just a timer that wasn't long enough for a busy (and, as I understand it, not all that fast) build host.

Denis, shall we merge this?

[infrastation]

I had in mind to understand this a bit better because recently I came across two other cases of a load instruction size mismatching the packet field size (pppoes uses ld for a 16-bit session ID, dpc and hdpc use ld for a 14-bit point code). Let me try tomorrow.

Other than that, this will need a change log entry.