Port security mode is used to disable address learning
at a port where an allow-source or allow-destination
MAC address filter is configured. A value of normal(1)
indicates that the port is not configured for security.
A value of secure-src-addrs(2) indicates that learning
for source addresses is disabled. A value of
secure-dest-addrs(3) indicates that learning for
destination addresses is disabled. A value of
secure-src-and-dest-addrs(4) indicates that learning is
disabled for both source and destination addresses.