bio/b_addr.c: resolve HP-UX compiler warnings.

bio/b_addr.c: resolve HP-UX compiler warnings.

The warning reads "[cast] may cause misaligned access". Even though
this can be application-supplied pointer, misaligned access shouldn't
happen, because structure type is "encoded" into data itself, and
application would customarily pass correctly aligned pointer. But
there is no harm in resolving the warning...

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5894)

(cherry picked from commit 55bd917bc4213bc668f48b87d8c6feb9918fef8f)