The isxdigit() checks in str2key() miss the required (unsigned char)
typecast. Also add int to the unsigned variable i.

Warning from gcc reported by goshhhy on github.
-- 
:wq Claudio

Index: parse.y
===================================================================
RCS file: /cvs/src/usr.sbin/bgpd/parse.y,v
diff -u -p -r1.455 parse.y
--- parse.y	16 Aug 2023 08:26:35 -0000	1.455
+++ parse.y	18 Mar 2024 10:15:13 -0000
@@ -4989,7 +4989,7 @@ expand_rule(struct filter_rule *rule, st
 int
 str2key(char *s, char *dest, size_t max_len)
 {
-	unsigned	i;
+	unsigned int	i;
 	char		t[3];
 
 	if (strlen(s) / 2 > max_len) {
@@ -5006,7 +5006,8 @@ str2key(char *s, char *dest, size_t max_
 		t[0] = s[2*i];
 		t[1] = s[2*i + 1];
 		t[2] = 0;
-		if (!isxdigit(t[0]) || !isxdigit(t[1])) {
+		if (!isxdigit((unsigned char)t[0]) ||
+		    !isxdigit((unsigned char)t[1])) {
 			yyerror("key must be specified in hex");
 			return (-1);
 		}