if_genet: Plug memory leaks
The rx_buf_tag should be checked when destroying rx dma mappings.
PR: 288309
Reviewed by: zlei
Submitted by: Mike Belanger <mibelanger@qnx.com>
MFC after: 3 days
(cherry picked from commit f46e95ae3addc9f7b975c187f71125825a38ffb1)