Those are not really relevant now, as no one would not install on a
machine with less than 512MB or 1G ram but stage2 currently takes 120MB
while we allow downloading it over HTTP if the machine has at least
68MB.

It was using the size of /proc/kcore which is 128T on x86_64
regardless of available memory, and does not exist on aarch64.

Instead use sysinfo().

dhcp.c: In function ‘parse_reply’:
dhcp.c:216:13: error: the comparison will always evaluate as ‘true’ for the address of ‘bootfile’ will never be NULL [-Werror=address]
  216 |         if (breq->bootfile && strlen(breq->bootfile) > 0) {
      |             ^~~~
dhcp.c:102:14: note: ‘bootfile’ declared here
  102 |         char bootfile[128];
      |              ^~~~~~~~
cc1: all warnings being treated as errors

Fix conflicts when rebasing after tmb changes