BUG/MEDIUM: ssl: Properly initialize msg_controllen.

When kTLS is compiled in, make sure msg_controllen is initialized to 0.
If we're not actually kTLS, then it won't be set, but we'll check that
it is non-zero later to check if we ancillary data.
This does not need to be backported.
This should fix CID 1620865, as reported in github issue #3106.

src/ssl_sock.c

@@ -344,7 +344,7 @@ static int ha_ssl_read(BIO *h, char *buf, int size)
 		struct cmsghdr hdr;
 		char buf[CMSG_SPACE(sizeof(unsigned char))];
 	} cmsgbuf;
-	size_t msg_controllen;
+	size_t msg_controllen = 0;
 #endif
 #endif
 	struct buffer tmpbuf;