bonding: move 802.3ad port state flags to uapi

The bond slave actor/partner operating state is exported as
bitfield to userspace, which lacks a way to interpret it, e.g.,
iproute2 only prints the state as a number:

ad_actor_oper_port_state 15

For userspace to interpret the bitfield, the bitfield definitions
should be part of the uapi. The bitfield itself is defined in the
802.3ad standard.

This commit moves the 802.3ad bitfield definitions to uapi.

Related iproute2 patches, soon to be posted upstream, use the new uapi
headers to pretty-print bond slave state, e.g., with ip -d link show

ad_actor_oper_port_state_str <active,short_timeout,aggregating,in_sync>

Signed-off-by: Andy Roulin <aroulin@cumulusnetworks.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>