- fix regression introduced in fping 4.3

bind to source only when option was set.
this allows to work in jails and lxc with custom IPs.
this allows IPv4 only and IPv6 only hosts

src/fping.c

@@ -995,11 +995,11 @@ int main(int argc, char** argv)
         exit(num_noaddress ? 2 : 1);
     }
 
-    if (socket4 >= 0) {
+    if (src_addr_set && socket4 >= 0) {
         socket_set_src_addr_ipv4(socket4, &src_addr, (socktype4 == SOCK_DGRAM) ? &ident4 : NULL);
     }
 #ifdef IPV6
-    if (socket6 >= 0) {
+    if (src_addr6_set && socket6 >= 0) {
         socket_set_src_addr_ipv6(socket6, &src_addr6, (socktype6 == SOCK_DGRAM) ? &ident6 : NULL);
     }
 #endif