net/qt4-network: fix openssl runtime linking

The PCBSD community discovered an issue with OpenSSL runtime linking, where
the OS bundled OpenSSL libraries are being loaded despite the user having
installed and selected a PORTS OpenSSL installation. The patch provided in
[1] resolves this by hard-coding the OpenSSL path to the default PREFIX of
/usr/local.

References:
[1] https://mail.kde.org/pipermail/kde-freebsd/2015-November/020535.html
PR: 209317
Submitted by: Kris Moore <kris@pcbsd.org>