ucode-mod-lua: add workaround for dynamic Lua extension loading

Reopen self with dlopen(RTLD_GLOBAL) in order to export liblua symbols for
runtime loading of dynamic Lua extensions.

Reported-by: Stijn Tintel <stijn@linux-ipv6.be>
Tested-by: Stijn Tintel <stijn@linux-ipv6.be>
Signed-off-by: Jo-Philipp Wich <jo@mein.io>