Description of problem:

Please help add the slave prio bond option. From [1]:

prio
	Slave priority. A higher number means higher priority.
	The primary slave has the highest priority. This option also
	follows the primary_reselect rules.

	This option could only be configured via netlink, and is only valid
	for active-backup(1), balance-tlb (5) and balance-alb (6) mode.
	The valid value range is a signed 32 bit integer.

	The default value is 0.

[1] https://www.kernel.org/doc/Documentation/networking/bonding.rst

Note: this option could only be set via netlink.