Additional devfs rulesets

[Warren Block]

devfsrules_jail is defined in /etc/defaults/devfs.rules, but a new 
ruleset is needed to unhide bpf devices for using check_dhcp in a jail.

It seems clunky to define the new ruleset in /etc/devfs.rules on the 
host.  Is there a more elegant way to define it with the jail (ezjail) 
settings in /usr/local/etc?

Although it would help with keeping devfs rules with the other jail 
settings, is the need for running services like dhcpd in a jail enough 
to justify adding a new ruleset for it to /etc/defaults/devfs.rules?

[devfsrules_jail_dhcp=5]
add include $devfsrules_jail
add path 'bpf*' unhide

(untested)