ipv4.c uses a gateway address of INADDR_NONE to represent "no
gateway".  It initialises the gateway address to INADDR_NONE before
calling fetch_ipv4_setting() to retrieve the configured gateway
address (if any).

However, as of commit 612f4e7 "[settings] Avoid returning
uninitialised data on error in fetch_xxx_setting()",
fetch_ipv4_setting() will zero the IP address if the setting does not
exist, rather than leaving it unaltered.

Fix by using a zero IP address to indicate "no gateway", so that a
non-existent gateway address setting will be treated as such.

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

reference holders that their reference is about to become invalid.

typical build will now include 880 bytes of PCI support code, compared to
2327 bytes in Etherboot 5.4.

(There is a slight cost of around 5 extra bytes per access to a
non-constant config space address; this should be an overall win.
Driver-specific accesses will usually be to constant addresses, for
which there is no additional cost.)

Yes, you really can do it in 65 bytes.