BUG/MEDIUM: proxy: use aligned allocations for struct proxy_per_tgroup

BUG/MEDIUM: proxy: use aligned allocations for struct proxy_per_tgroup

In 3.2, commit f879b9a18 ("MINOR: proxies: Add a per-thread group field
to struct proxy") introduced struct proxy_per_tgroup that is declared as
thread_aligned, but is allocated using calloc(). Thus it is at risk of
crashing on machines using instructions requiring 64-byte alignment such
as AVX512. Let's use ha_aligned_zalloc_typed() instead of malloc().

For 3.2, we don't have aligned allocations, so instead the THREAD_ALIGNED()
will have to be removed from the struct definition. Alternately, we could
manually align it as is done for fdtab.