queue has its own interrupt. If the exact number that we need is not a
power of 2 and we're using MSI, then switch to interrupt multiplexing.
While here, replace the magic numbers with something more readable.
MFC after: 3 days
- everything related to LRO should be in #ifdef INET blocks
- reorder sge_iq's fields so that the most frequently used are all together
- pull all rx code into t4_intr_data directly
- let go of the ingress queue lock when passing up data
- refill the freelist only if it is short of at least 32 buffers
