python3: fix build with SSL module
No idea how this creeped up. Probably OpenSSL been has updated recently.
Will send this patch upstream as well, but in the meantime we should fix
the Python3 build.
Build error seems to be:
```
<openwrt>/build_dir/target-i386_pentium4_musl/Python-3.7.0/Modules/_ssl.c:4000:5: error: implicit declaration of function 'DH_free'; did you mean 'lh_free'? [-Werror=implicit-function-declaration]
DH_free(dh);
^~~~~~~
lh_free
cc1: some warnings being treated as errors
Python build finished successfully!
The necessary bits to build these optional modules were not found:
_tkinter _uuid nis
To find the necessary bits, look in setup.py in detect_modules() for the module's name.
The following modules found by detect_modules() in setup.py, have been
built by the Makefile instead, as configured by the Setup files:
_abc atexit pwd
time zlib
Failed to build these modules:
_ssl
Makefile:618: recipe for target 'sharedmods' failed
```
Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>