rc.d: Introduce 'dhcp_client' to wrap over dhclient and dhcpcd

The new 'dhcp_client' rc script is a wrapper to start either dhclient(8)
or dhcpcd(8) based on the value of the 'dhcp_client' rc variab

rc.d: Introduce 'dhcp_client' to wrap over dhclient and dhcpcd

The new 'dhcp_client' rc script is a wrapper to start either dhclient(8)
or dhcpcd(8) based on the value of the 'dhcp_client' rc variable.

Other rc scripts are updated to depend on this wrapper instead of the
explicit 'dhclient'. This eases the migration from dhclient(8) to
dhcpcd(8) later.

Update rc.conf.5 and dhcp.8 man pages accordingly.

Meanwhile, remove the two obsolete variables 'dhcp_{program,flags}' from
/etc/rc.subr.

show more ...

Point to more neutral, yet dports biased directories from manual pages.

Most of them are identical in pkgsrc.

Fix another path

Fix path to the dhcpd.conf file.

Add dhcp(8) which gives some general info on DHCP client/server
configuration.

Adapted-from: OpenBSD