ovs-lldp: Use better types for ISID and VLANs.

ovs-lldp: Use better types for ISID and VLANs.

An ISID is 24 bits, so it fits in a uint32_t.  A VLAN is 12 bits, so it
fits in a uint16_t.  Use these types consistently, instead of int64_t.

This removes a check in aa_mapping_unregister() that seems a little
mysterious to me: it previously checked for ISID and VLAN values >= 0.  I
don't see a way that they could be < 0 in this situation though.

Signed-off-by: Ben Pfaff <blp@nicira.com>