ipappend: clean up ipappend code; add ipappend to plain cmdline

ipappend: clean up ipappend code; add ipappend to plain cmdline

ipappend information is needed for the plain cmdline too, since it may
be used by linux.c32.  While we're at it, clean up the handling of
ipappend lines -- we can rather obviously use a loop for them.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>