net: Increase the default network connection count

For dual IPv6 and IPv4 stack, the limit of network connections needs
to be increased as the default value of 4 is too small in this case.

Change-Id: If031ae9ee1dd095d20ee6a677ef8c678055ecfb0
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>