Add a driver using libslirp to provide a virtual network interface
without requiring root permissions on the host. This simplifies the
process of running iPXE as a Linux userspace application with network
access. For example:
make bin-x86_64-linux/slirp.linux
./bin-x86_64-linux/slirp.linux --net slirp
libslirp will provide a built-in emulated DHCP server and NAT router.
Settings such as the boot filename may be controlled via command-line
options. For example:
./bin-x86_64-linux/slirp.linux \
--net slirp,filename=http://192.168.0.1/boot.ipxe
Signed-off-by: Michael Brown <mcb30@ipxe.org>