Do not define __NO_STRICT_ALIGNMENT for armv6. While the requirements
are no longer natural-alignment strict, there are still some restrictions.

FreeBSD network code assumes data is naturally-aligned or is running
on a platform with no restrictions; pointers are not annotated to
indicate the data pointed to may be packed or unaligned. The clang
optimizer can sometimes combine the load or store of a pair of adjacent
32-bit values into a single doubleword load/store, and that operation
requires at least 4-byte alignment. __NO_STRICT_ALIGNMENT can lead
to tcp headers being only 2-byte aligned.

Note that alignment faults remain disabled on armv6, this change reverts
only the defining of the symbol which leads to some overly-agressive code
shortcuts when building common/shared drivers and network code for arm.

Approved by: re(kib)