bsdinstall: draw attention to new network config options

The network configuration options have changed in bsdinstall, with
an Auto option to proceed directly to DHCP and IPv6 autoconfig (which
is the default) as well as Manual (the old mode). For users like me
that were used to hitting return automatically to select an interface,
but want manual configuration, attempt to call out the difference:
Change the menu caption to say "Please select a network interface
and configuration mode:" and not just an interface.

Reviewed by: jrtc27