Some software #includes opensslconf.h which typically contains settings that we
put in opensslfeatures.h (a header name not in OpenSSL). Rename it to
opensslconf.h.
Change-Id: Icd21dde172e5e489ce90dd5c16ae4d2696909fb6
Reviewed-on: https://boringssl-review.googlesource.com/7216
Reviewed-by: Adam Langley <agl@google.com>
