lib/socket: Fix improper use of default interface speed

lib/socket: Fix improper use of default interface speed

_get_interfaces() function from interfaces.c uses if_speed
variable to store interface speed and is initialized with a
default value at start. But if_speed populated via one
iteration for a specific IP address will be treated as the
default value for next iteration which is wrong. Therefore
change is to move the initialization cum declaration of
if_speed inside iteration of IP addresses loop.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11734

Signed-off-by: Anoop C S <anoopcs@redhat.com>
Reviewed-by: Michael Adam <obnox@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Autobuild-User(master): Michael Adam <obnox@samba.org>
Autobuild-Date(master): Sat Feb 13 16:22:22 CET 2016 on sn-devel-144