size in terms of lines (instead of bytes). When changing video mode
in ioctl SW_XXX commands, syscons checks scp->history_size and
allocate a history buffer at least as large as the new screen size.
(This was unnecessary before, because HISTORY_SIZE was as large as 100
lines and this is bigger than the maximum screen size: 60 lines).
Similar adjustment is done in ioctl CONS_HISTORY command too.
PR: kern/4169
Reviewed by: sos
ec0b9f839d