Explicitly recognize fe80::/64 as 'local'

For various reasons, it is likely/expected for fe80:: to fail the 'local'
check. This is fine in most contexts, except for credserver and ssdp.

ssdp already special cased fe80::, so special case fe80:: in credserver
as well.

confluent_server/confluent/credserver.py

@@ -43,6 +43,8 @@ libc = ctypes.CDLL(ctypes.util.find_library('c'))
 
 
 def address_is_somewhat_trusted(address, nodename, cfm):
+    if netutil.ip_on_same_subnet(address.split('%')[0], 'fe80::', 64):
+        return True
     if netutil.address_is_local(address):
         return True
     authnets = cfm.get_node_attributes(nodename, 'trusted.subnets')