rpcsec_tls/client: API refactoring between kernel and rpc.tlsclntd(8)

Now that the conversion of rpcsec_tls/client + rpc.tlsclntd(8) to the
netlink(4) socket as RPC transport started using kernel socket pointer as
a reliable cookie, we can shave off quite a lot of complexity. We will
utilize the same kernel-generated cookie in all RPCs. And the need for
the daemon generated cookie in the form of timestamp+sequence vanishes.

In the clnt_vc.c we no longer need to store the userland cookie, but we
still need to observe the TLS life cycle of the client. We observe
RPCTLS_INHANDSHAKE state, that lives for a short time when the socket had
already been fetched by the daemon with the syscall, but the RPC call is
still waiting for the reply from daemon.

This time bump the RPC version.

Reviewed by: rmacklem
Differential Revision: https://reviews.freebsd.org/D48564