[2.7] bpo-35264: Modules/_ssl.c: fix build with OpenSSL 1.1.0 (GH-10570)

[2.7] bpo-35264: Modules/_ssl.c: fix build with OpenSSL 1.1.0 (GH-10570)

Fixes a build error with OpenSSL 1.1.0. There is already code in the
`_ssl.c` that handles all the weird cases of the NPN config macros (with
various OpenSSL & LibreSSL versions).
That code will provide a HAVE_NPN variable, which should be used in the
rest of the code to check whether (or what) to compile regarding NPN.

This change adds HAVE_NPN in the remaining places where it should have been
placed.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
https://bugs.python.org/issue35264