gnu: wpa_supplicant: Update to 2.8 [security fixes].

gnu: wpa_supplicant: Update to 2.8 [security fixes].

This release fixes CVE-2019-9494, CVE-2019-9495, CVE-2019-9496, CVE-2019-9497,
CVE-2019-9498, CVE-2019-9499, and CVE-2019-11555.

* gnu/packages/admin.scm (wpa-supplicant-minimal): Update to 2.8.
[source](snippet): New field.  Disable D-Bus.
[arguments]: Change CONFIG_TLS to use OpenSSL rather than GnuTLS.  This is
required by many of the new default build-time settings.
[inputs]: Remove GNUTLS and LIBGCRYPT.  Add OPENSSL.
(wpa-supplicant)[arguments]: Remove obsolete CONFIG_CTRL_IFACE_DBUS=y.