FROMLIST: export: fix string handling of namespace in EXPORT_SYMBOL_NS

Commit c3a6cf19 ("export: avoid code duplication in
include/linux/export.h") broke the ability for a defined string to be
used as a namespace value.  Fix this up by adding another layer of
indirection to preserve the previous functionality.

Fixes: c3a6cf19 ("export: avoid code duplication in include/linux/export.h")
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Matthias Maennich <maennich@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220108140415.3360088-1-gregkh@linuxfoundation.org


Bug: 210074446
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ie43aa24f64b55cd1d70161c906b0ef32610430aa