Because nfe(4) hardware doesn't support SG on Rx path, supporting
jumbo frame requires very large contiguous kernel memory(i.e. several
mega bytes). In case of lack of contiguous kernel memory that
allocation request may always fail. However nfe(4) can operate on normal
sized MTU frames, so go ahead and just disable jumbo frame support.
While I'm here add a new tunable "hw.nfe.jumbo_disable" to disable
jumbo frame support.
In nfe_poll, make sure to invoke correct Rx handler.
Approved by: re (kensmith)
8b590ad2d1