BUILD: ssl: fix typo in HAVE_SSL_CTX_ADD_SERVER_CUSTOM_EXT macro

HAVE_SSL_CTX_ADD_SERVER_CUSTOM_EXT was introduced in ec609098718b9c1cd803ca57442b2b98c9ba4a16
however it was defined as HAVE_SL_CTX_ADD_SERVER_CUSTOM_EXT (missing "S")
let us fix typo

(cherry picked from commit 7bbf5866e011d22ee8f1d00471ce330cc72dcd0e)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index df5987d..b9d52ee 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -1457,7 +1457,7 @@
 #endif
 
 
-#ifdef HAVE_SL_CTX_ADD_SERVER_CUSTOM_EXT
+#ifdef HAVE_SSL_CTX_ADD_SERVER_CUSTOM_EXT
 
 #define CT_EXTENSION_TYPE 18
 
@@ -3130,7 +3130,7 @@
 	}
 #endif
 
-#ifdef HAVE_SL_CTX_ADD_SERVER_CUSTOM_EXT
+#ifdef HAVE_SSL_CTX_ADD_SERVER_CUSTOM_EXT
 	if (sctl_ex_index >= 0 && ckch->sctl) {
 		if (ssl_sock_load_sctl(ctx, ckch->sctl) < 0) {
 			memprintf(err, "%s '%s.sctl' is present but cannot be read or parsed'.\n",