mlx5e: Make TLS tag zones unmanaged

These zones are cache zones used to allocate TLS offload contexts from
firmware. Releasing items from the cache is a sleepable operation due
to the need to await a response from the firmware command freeing the
tag, so items cannot be reclaimed from the zone in non-sleepable
contexts. Since the cache size is limited by firmware limits, avoid
this by setting UMA_ZONE_UNMANAGED to avoid reclamation by uma_timeout()
and the low memory handler.

Reviewed by: hselasky, kib
MFC after: 3 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D34142