mount/conf: avoid creating temporary object

instead of creating an empty string and then mutating it, just
assign the return value of `eaddr.ip_n_port_to_str()` to it.
as C++17 enforces copy ellision in this case, we can avoid
two unnecessary calls here:

- creating a temporary object and destroying it.
- memcpy the temporary object.

also, after this change, the code is simpler.

Signed-off-by: Kefu Chai <[email protected]>

src/mount/conf.cc

@@ -70,8 +70,7 @@ extern "C" void mount_ceph_get_config_info(const char *config_file,
 	continue;
     }
 
-    std::string addr;
-    addr += eaddr.ip_n_port_to_str();
+    std::string addr = eaddr.ip_n_port_to_str();
     /* If this will overrun cci_mons, stop here */
     if (monaddrs.length() + 1 + addr.length() + 1 > sizeof(cci->cci_mons))
       break;