resolve: bump *_SEARCH_DOMAIN_MAX to 1024

As prompted by #38393, search domains may be large when a complicated
network setting is used, especially when VPN is used. Let's bump the
limit to 1024.

Note, this does not bump the maximum number of DNS servers, as setting
thousands of DNS servers is spurious and mostly meaningless. Let's keep
the maximum for a while until someone requests to also bump them.

Continuation of b950ee06e6.

Closes #38393.

src/resolve/resolved-dns-delegate.h

@@ -4,7 +4,7 @@
 #include "list.h"
 #include "resolved-forward.h"
 
-#define DELEGATE_SEARCH_DOMAINS_MAX 256
+#define DELEGATE_SEARCH_DOMAINS_MAX 1024
 #define DELEGATE_DNS_SERVERS_MAX 256
 
 /* A DnsDelegate object is used to manage additional, explicitly configured unicast DNS lookup scopes,

src/resolve/resolved-link.h

@@ -9,7 +9,7 @@
 #include "resolve-util.h"
 #include "resolved-forward.h"
 
-#define LINK_SEARCH_DOMAINS_MAX 256
+#define LINK_SEARCH_DOMAINS_MAX 1024
 #define LINK_DNS_SERVERS_MAX 256
 
 typedef struct LinkAddress {

src/resolve/resolved-manager.h

@@ -15,7 +15,7 @@
 #include "resolved-etc-hosts.h"
 #include "resolved-forward.h"
 
-#define MANAGER_SEARCH_DOMAINS_MAX 256
+#define MANAGER_SEARCH_DOMAINS_MAX 1024
 #define MANAGER_DNS_SERVERS_MAX 256
 
 typedef struct Manager {