MFC r245848 (by jhb):

MFC r245848 (by jhb):
Always update the hw.uart.console hint anytime a change is made to the
comconsole setup.  Previously the hint would be set when if you set a
custom port, but it would not be updated if you later set a custom speed.

Also, leave the hw.uart.console hint mutable so it can be overridden or
unset by the user if needed.

git-svn-id: svn://svn.freebsd.org/base/stable/9@260868 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f