Update the OpenVPN package to version 2.4.6, refresh patches and drop
menuconfig options which are not supported upstream anymore.
Also fix the x509-alt-username configure flag - it is not supported
by mbedtls and was syntactically wrong in the Makefile - and the
port-share option which has been present in menuconfig but not been
used in the Makefile.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>