net80211: move net_epoch into net80211

[bz]

Summary

Move the net_epoch into net80211 around the if_input calls and out of
the driver (in this first case LinuxKPI). This reduces coverage but
also allows us to alloc in calls like (*ampdu_rx_start) which do not
actually pass data up the stack.

This reverts b65f813c1ab99448278961c5ca80dc422b1eae29, 21c4082de9e2cf9a0fd81a9a981ab06022956847, 17c328b6aebfa03cd1c2cbfbbc617e3b341bf1e4, af2441fbc7fa9e522e7f8697e5a181bdd4ff9e00, and 6c3e93cb5a4aa4b8a2d8d4d326f2a7c34d3a4458 for ath.

Sposnored by: The FreeBSD Foundation
MFC after: 3 days

Test Plan

For people to review and test the entire change.

[adrian]

I think it's fine, it just means we can't batch a single epoch call inside the driver when it does encap/decap for us!

[bz]

Add all the reverts I could find needed for wirelress drivers so people can
better review and test. My builds are currently running.

• Revert "Widen EPOCH(9) usage in PCI WLAN drivers."
• Revert "Widen EPOCH(9) usage in USB WLAN drivers."
• Revert "Enter the network epoch in USB WiFi drivers when processing input"
• Revert "[ath] Attempt to fix epoch handling."
• ath: Revert "Use NET_TASK_INIT() and NET_GROUPTASK_INIT() for drivers that process"