[tcp] Do not send RST for unrecognised connections

On large networks with substantial numbers of monitoring agents,
unwanted TCP connection attempts may end up flooding iPXE's ARP cache.

Fix by silently dropping packets received for unrecognised TCP
connections.  This should not cause problems, since many firewalls
will also silently drop any such packets.

Reported-by: Jarrod Johnson <jarrod.b.johnson@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
[tcp] Fix comment to match code behaviour

Reported-by: Thomas Miletich <thomas.miletich@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
[test] Add self-tests for base16

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[base16] Generalise base16_decode() to hex_decode()

Provide a generic hex_decode() routine which can be shared between the
Base16 code and the "hex" and "hexhyp" settings parsers.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[settings] Use hex_decode() to parse hex settings

Use hex_decode() to parse "hex" and "hexhyp" settings.  Note that this
parser is stricter than the old parser; it now requires exactly two
hex digits for each byte.  (The old parser was based upon strtoul()
and so would allow leading whitespace and a leading plus or minus
sign.)

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[settings] Add "hexraw" setting type

Originally-implemented-by: Jeppe Toustrup <ipxe@tenzer.dk>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
[netdevice] Add "bustype" and "busloc" settings

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[settings] Add "busdevfn" setting type

Allow network device's "busloc" setting to be formatted as a PCI
bus:dev.fn address using e.g. ${net0/busloc:busdevfn}.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[linux] Add support for accessing PCI configuration space via /proc/bus/pci

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[settings] Add config/settings.h

Move VMWARE_SETTINGS build configuration option from config/sideband.h
to a new config/settings.h.

Existing instances of config/local/sideband.h will not be affected,
since config.c still #includes config/sideband.h.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
[settings] Expose PCI configuration space via settings mechanism

Allow values to be read from PCI configuration space using the syntax

  ${pci/<busdevfn>.<offset>.<length>}

where <busdevfn> is the bus:dev.fn address of the PCI device
(expressed as a single integer, as returned by ${net0/busloc}),
<offset> is the offset within PCI configuration space, and <length> is
the length within PCI configuration space.

Values are returned in reverse byte order, since PCI configuration
space is little-endian by definition.

Signed-off-by: Michael Brown <mcb30@ipxe.org>