Fix building unit tests via contrib/ports/unix/check on Debian 9, gcc 6.3.0.
Fixes:
<snip>/ip_addr.h:105:58: error: the comparison will always evaluate as ‘true’ for the address of ‘ip1’ will never be NULL [-Werror=address]
#define IP_SET_TYPE(ipaddr, iptype) do { if((ipaddr) != NULL) { IP_SET_TYPE_VAL(*(ipaddr),iptype); }}while(0)
Signed-off-by: Jacob Kroon <jacob.kroon@gmail.com>