netfilter: ipset: Add hash: fix coccinelle warnings

netfilter: ipset: Add hash: fix coccinelle warnings

net/netfilter/ipset/ip_set_hash_netnet.c:115:8-9: WARNING: return of 0/1 in function 'hash_netnet4_data_list' with return type bool
/c/kernel-tests/src/cocci/net/netfilter/ipset/ip_set_hash_netnet.c:338:8-9: WARNING: return of 0/1 in function 'hash_netnet6_data_list' with return type bool

Return statements in functions returning bool should use
true/false instead of 1/0.
Generated by: coccinelle/misc/boolreturn.cocci

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>