I reverted those masking changes in Fedora and the baffling problem
with 3Com 3C905 network adapters went away.
Before, they would print:
eth0: transmit timed out, tx_status 00 status e601.
diagnostics: net 0ccc media 8880 dma 0000003a fifo 0000
eth0: Interrupt posted but not delivered -- IRQ blocked by another device?
Flags; bus-master 1, dirty 295757(13) current 295757(13)
Transmit list 00000000 vs. f7150a20.
0: @f7150200 length 80000070 status 0c010070
1: @f71502a0 length 80000070 status 0c010070
2: @f7150340 length 8000005c status 0c01005c
Now they just work, apparently...
So why not just revert the change?