o remove irrlevant spl
Notes:
1. We don't lock domain list traversals as this is safe until we start
removing domains.
2. The calculation of max_datalen in net_init_domain appears safe as
noone depends on max_hdr and max_datalen having consistent values.
3. Giant is still held for fast and slow timeouts; this must stay until
each timeout routine is properly locked (coming soon).
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