MDEV-19510 Issue with: sql/wsrep_mysqld.cc : ip_len

Patch `36a2a185` introduced `wsrep_server_incoming_address()` in `10.4`.
Since AIX `/usr/include/netinet/ip.h` header defines `ip_len` as `ip_ff.ip_flen`
and `size_t const ip_len` is preprocessed as `size_t const ip_ff.ip_vhltl.ip_x.ip_xlen`,
to prevent the define from overwriting code in MariaDB,
rename the variable name to `ip_len_mdb`.

This patch is done by Tony Reix <tony.reix@atos.net>.
This patch was submitted under MCA.
Closes #1307

sql/wsrep_mysqld.cc

@@ -550,11 +550,11 @@ static std::string wsrep_server_incoming_address()
     {
       if (node_addr.size())
       {
-        size_t const ip_len= wsrep_host_len(node_addr.c_str(), node_addr.size());
-        if (ip_len + 7 /* :55555\0 */ < inc_addr_max)
+        size_t const ip_len_mdb= wsrep_host_len(node_addr.c_str(), node_addr.size());
+        if (ip_len_mdb + 7 /* :55555\0 */ < inc_addr_max)
         {
-          memcpy (inc_addr, node_addr.c_str(), ip_len);
-          snprintf(inc_addr + ip_len, inc_addr_max - ip_len, ":%u",
+          memcpy (inc_addr, node_addr.c_str(), ip_len_mdb);
+          snprintf(inc_addr + ip_len_mdb, inc_addr_max - ip_len_mdb, ":%u",
                    (int)mysqld_port);
         }
         else