Change UEFI ipxe bootloader default

The bootloader default for ipxe, previously set to ipxe.efi
was, while consistent with the interface naming, a likely
setting that had to be overridden by most deployments,
as very little hardware can make use of ipxe.efi for network
booting, where as snponly.efi is realistically what should
be used in nearly all cases with the exception of some
extremely early UEFI supporting hardware, which may
happen to work with ipxe.efi *if* support for the network
card happens to be compiled in.

Note: This was likely never observable in CI as CI leverages
firmware with integrated iPXE binaries.

Change-Id: I808cf92c98339aa447b4799900066c310e15fd5b

ironic/conf/pxe.py

@@ -119,10 +119,10 @@ opts = [
                default='undionly.kpxe',
                help=_('Bootfile DHCP parameter.')),
     cfg.StrOpt('uefi_ipxe_bootfile_name',
-               default='ipxe.efi',
+               default='snponly.efi',
                help=_('Bootfile DHCP parameter for UEFI boot mode. If you '
                       'experience problems with booting using it, try '
-                      'snponly.efi.')),
+                      'ipxe.efi.')),
     cfg.DictOpt('pxe_bootfile_name_by_arch',
                 default={},
                 help=_('Bootfile DHCP parameter per node architecture. '

releasenotes/notes/change-ipxe-default-file-a9ed5e17fc3d022e.yaml

@@ -0,0 +1,10 @@
+---
+upgrade:
+  - |
+    The default UEFI iPXE bootloader, ``[pxe]uefi_ipxe_bootfile_name`` used
+    by the ``ipxe`` boot interface, has been changed from ``ipxe.efi`` to
+    ``snponly.efi``. This is because most deployments actually need to use
+    ``snponly.efi`` as it contains support for the UEFI integrated network
+    stack, where as ``ipxe.efi`` does not and only contained compiled in
+    network drivers, for UEFI, there happen to be few as the UEFI
+    standard requires networking to be handled by the UEFI firmware.