Some shuffling around of the image management code; this needs tidying up.

list.

Added FEATURE() macros to most relevant (non-driver) files.

and generate DHCP options to indicate features to DHCP server (and to
PXE NBPs).

This reverts commit 3cb133d27d.

tcpip_tx().  This avoids the irritating wait when you accidentally type
"kernel pxelinux.0" before bringing up the network interface.

Add ENETUNREACH to strerror()'s list.

"kernel".

strerror(rc) in their closed() methods without producing "Error
0x0000" when the connection is closed normally.

can't modify it).

names.

Add "dev" pointer in struct net_device to tie network interfaces back to a
hardware device.

Force natural alignment of data types in __table() macros.  This seems to
prevent gcc from taking the unilateral decision to occasionally increase
their alignment (which screws up the table packing).

it's a serial console and remembers state from the previous program
run.