fetch: pass --ipv4 and --ipv6 options to sub-fetches

fetch: pass --ipv4 and --ipv6 options to sub-fetches

The options indicate user intent for the whole fetch operation, and
ignoring them in sub-fetches (i.e. "--all" and recursive fetching of
submodules) is quite unexpected when, for instance, it is intended
to limit all of the communication to a specific transport protocol
for some reason.

Signed-off-by: Alex Riesen <alexander.riesen@cetitec.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>