outbound: fix build on xenial
> outbound_mod.c: In function 'mod_init':
> outbound_mod.c:122:2: error: too many arguments to function 'mod_init_openssl'
> mod_init_openssl(NULL);
> ^
> outbound_mod.c:82:13: note: declared here
> static void mod_init_openssl(void)
^