MFC r308700:
[etherswitch] add RTL8366SR support
Add RTL8366SR support at etherswitch driver. Tested on RTL8366RB and
RTL8366SR.
Submitted by: Hiroki Mori <yamori813@yahoo.co.jp>
Reviewed by: adrian, mizhka
Approved by: adrian(mentor)
Differential Revision: https://reviews.freebsd.org/D6796