Updated commit message.

Do I need a more elaborate commit message here, too?

In D46564#1064476, @corvink wrote:

Where's the commit message?

"-cp" is already illegal, see the check on line 303 and 304, so nothing changes in that regard. Also, "-r cannot be used with -c, -d, -n, or -p" already. I also see no "-h" option, so no "-ch" either, or am I missing anything here?

Add more elaborate commit message. Remove the extra empty line.

Fix manpage as suggested by Corvin.
No longer get the cmd length from the request header as the CRB emulation should pass the correct length instead.

Even FreeBSD's own TPM driver writes the INT_ENABLE register during attach, writing 0 to make sure interrupts are off. bhyve really shouldn't crash the VM when that happens.

Document the swtpm backend in bhyve.8 and bhyve_config.5.