ceph.spec.in: increase memory per core to 3000MB on SUSE distros

ceph.spec.in: increase memory per core to 3000MB on SUSE distros

in the KVM instance offered by OBS, we have

[  346s] + cat /proc/meminfo
[  347s] MemTotal:       10167736 kB
[  347s] MemFree:         4983964 kB
[  347s] MemAvailable:    9826800 kB
[  347s] Buffers:           85856 kB
[  347s] Cached:          4615192 kB
[  347s] SwapCached:            0 kB
...
[  347s] SwapTotal:       2097148 kB

and its number of hardware threads is

[  346s] ++ /usr/bin/getconf _NPROCESSORS_ONLN
[  346s] + _threads=8

so ($MemTotal+$SwapTotal)/1024/2600 = 4.6, which is less
than the # of threads, so "4" was used for the number of jobs.

but per our recent observation in
38be14bc0fa32be6877dea08ebd35495d39e464f, some compiling jobs could
take up to 3GB. in the OOM failure in OBS, we had

[24915s] [24848.843594] Out of memory: Killed process 16894 (cc1plus) total-vm:4293756kB, anon-rss:2970012kB, file-rss:0kB, shmem-rss:0kB, UID:399 pgtables:8324kB oom_score_adj:0

where 4GiB memory was allocated, in which 3GiB was mapped into
memory. this matches with our findings.

in this change, the memory per core is bumped up to 3000MB
in hope to address the OOB. the downside of this change is
that it would take even longer to finish the build if the
building host is limited in memory.

Signed-off-by: Kefu Chai <kchai@redhat.com>