aq_isc_rxd_pkt_get() returned EBADMSG when a receive descriptor's
MAC/receive-error bit (rx_stat bit 0) was set. iflib treats any error
from isc_rxd_pkt_get() as a fatal ring fault and answers with
IFC_DO_RESET -- a full interface reinitialization. A per-frame receive
error is not a ring fault: on a marginal link or cable the Atlantic
delivers errored frames continuously, so each one triggered another
reset and the interface reset-stormed itself into carrying no traffic
instead of merely dropping the bad frames.

The Atlantic delivers errored frames to the host by design (Linux drops
them in software via buff->is_error), and iflib offers no per-frame
error return that isn't a reset. Follow the vmxnet3 model: on a receive
error zero the fragment lengths and return success. iflib then discards
the packet (assemble_segments() excludes zero-length fragments) while
still recycling the descriptors through the refill path -- no reset.
Also drop frames flagged with an RX-DMA fault (rdm_err), not just the
MAC-error bit; and keep iri_len non-zero on that drop path, since iflib
asserts iri_len != 0.

The genuinely structural errors -- more segments than isc_rx_nsegments,
or a pkt_len inconsistent with the descriptor count -- still return
EBADMSG, since those indicate a confused ring where a reset is the right
recovery.