ui: import: increase CPU limits to better match ESXi

ui: import: increase CPU limits to better match ESXi

On ESXi one can have at max 768 vCPUs and that over maximal 128
sockets. Further, by default ESXi will favor adding single-cpu
sockets, so if one just enters "give me 8 vCPUs", it will be 8
single-core sockets.

As we only supported up to 4 sockets in the web UI, which caused this
field to show up as invalid on initial load for such VMs, which is not
nice.

Having that many sockets is rather odd, so for us it doesn't make
sense to allow more than the ESXi limit that, but having more vCPUs
might make sense, so allow up to 1024 for that for now.

Note that QEMU and our API backend doesn't really cares, the kernels
NR_MAX_CPU is the limit there. Albeit it is questionable if using more
vCPU threads as there are host threads has some sense in any setup.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>