Here go cons of using inpcb for divert:
- divert(4) uses only 16 bits (local port) out of struct inpcb,
which is 424 bytes today.
- The inpcb KPI isn't able to provide hashing for divert(4),
thus it uses global inpcb list for lookups.
- divert(4) uses INET-specific part of the KPI, making INET
a requirement for IPDIVERT.
Maintain our own very simple hash lookup database instead. It
has mutex protection for write and epoch protection for lookups.
Since now so->so_pcb no longer points to struct inpcb, don't
initialize protosw methods to methods that belong to PF_INET.
Also, drop support for setting options on a divert socket. My
review of software in base and ports confirms that this has no
use and unlikely worked before.
Differential revision: https://reviews.freebsd.org/D36382
f1fb051716