MINOR: log: slightly improve error message syntax on log failure

The error messages used to say something along "socket logger 2 failed"
or "sendmsg logger 2 failed" which are confusing. Let's rephrase this
"sendmsg() failed for logger 2".
diff --git a/src/log.c b/src/log.c
index 8edb1b7..24e4c3f 100644
--- a/src/log.c
+++ b/src/log.c
@@ -1346,7 +1346,7 @@
 
 				if (!once) {
 					once = 1; /* note: no need for atomic ops here */
-					ha_alert("socket for logger #%d failed: %s (errno=%d)\n",
+					ha_alert("socket() failed in logger #%d: %s (errno=%d)\n",
 					         nblogger, strerror(errno), errno);
 				}
 				continue;
@@ -1480,7 +1480,7 @@
 
 			if (!once) {
 				once = 1; /* note: no need for atomic ops here */
-				ha_alert("sendmsg logger #%d failed: %s (errno=%d)\n",
+				ha_alert("sendmsg() failed in logger #%d: %s (errno=%d)\n",
 				         nblogger, strerror(errno), errno);
 			}
 		}