[net80211] check IBSS SSID before adding nodes discovered by beacons/probe requests.

[adrian]

Summary

IBSS merging requires "all BSSID" beacons are received. However, this populates
a lot of nodes in the node table for peers that are not us.

This code adds a simple (!) SSID string check against the scan parameters SSID.
If it's found to match, the node is allowed.

This needs a /lot/ more testing before I'm comfortable landing it in -HEAD.

Test Plan

• AR9380 in IBSS mode on a very busy office IBSS network. SSID mismatches don't populate neighbor entries; SSID matches do.

[adrian]

(The reason for the gotos is I'm going to add debugging there before they return.)

[avos]

sys/net80211/ieee80211_node.c

607

'!!' (or '== 0') is not necessary; one of them may be removed.

[avos]

Works fine when 'hidessid' is not set (however, 'hidessid' bug is not related to this change).