submodule: only preserve flags across recursive status/update invocations

Recursive invocations of submodule update/status preserve all arguments,
so executing

        git submodule update --recursive -- foo

attempts to recursively update a submodule named "foo".

Naturally, this fails as one cannot have an infinitely-deep stack of
submodules each containing a submodule named "foo". The desired behavior
is instead to update foo and then recursively update all submodules
inside of foo.

This commit accomplishes that by only saving the flags for use in the
recursive invocation.

Signed-off-by: Kevin Ballard <kevin@sb.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>