cgrulesengd: Fix the return value check in recvfrom

In cgre_receive_netlink_msg::recvfrom(), the return value recv_len is
checked against ENOBUFS, which is an errno value that represents the
last occurred error. However, this comparison has two issues:

First, if the recv_len message bytes are equal to the value of ENOBUFS,
it will return a false positive error.

Second, recv_len is not checked for -1, which indicates an unexpected
event that requires investigation. Fortunately, the next line acts as a
safety net, returning on error conditions and EOF.

Fix this by checking for -1 (error) and comparing errno against ENOBUFS.

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>

Author: kamalesh-babulal

src/daemon/cgrulesengd.c

@@ -567,7 +567,7 @@ static int cgre_receive_netlink_msg(int sk_nl)
 	from_nla_len = sizeof(from_nla);
 	recv_len = recvfrom(sk_nl, buff, sizeof(buff), 0, (struct sockaddr *)&from_nla,
 			    &from_nla_len);
-	if (recv_len == ENOBUFS) {
+	if (recv_len == -1 && errno == ENOBUFS) {
 		flog(LOG_ERR, "ERROR: NETLINK BUFFER FULL, MESSAGE DROPPED!\n");
 		return 0;
 	}