Improve L2FIB delete entry handling and "show l2fib" CLI options

Improve L2FIB delete entry handling and "show l2fib" CLI options

Improve deletion of L2FIB MAC entry using l2fib_add_del API. If
sw_if_index param specified in th API is non-zero, check that its
value match that of the MAC entry to proceed with deletion.

Improve "show l2fib" CLI to allow display of all entries, learned
entries only, or added ovia CLI/API entries only. For added entry,
show "no" under the age column to indicate entry does not age.

Change-Id: I0bd2582c2b6bac268e551e4f8ca6dab2be4400ad
Signed-off-by: John Lo <loj@cisco.com>