resolved: define various packet sizes as unsigned

This seems like the right thing to do, and apparently at least some compilers
warn about signed/unsigned comparisons with DNS_PACKET_SIZE_MAX.

src/resolve/resolved-dns-packet.c

@@ -28,7 +28,7 @@
 
 #define EDNS0_OPT_DO (1<<15)
 
-#define DNS_PACKET_SIZE_START 512
+#define DNS_PACKET_SIZE_START 512u
 assert_cc(DNS_PACKET_SIZE_START > UDP_PACKET_HEADER_SIZE)
 
 typedef struct DnsPacketRewinder {

src/resolve/resolved-dns-packet.h

@@ -58,13 +58,13 @@ struct DnsPacketHeader {
 /* The various DNS protocols deviate in how large a packet can grow,
    but the TCP transport has a 16bit size field, hence that appears to
    be the absolute maximum. */
-#define DNS_PACKET_SIZE_MAX 0xFFFF
+#define DNS_PACKET_SIZE_MAX 0xFFFFu
 
 /* RFC 1035 say 512 is the maximum, for classic unicast DNS */
-#define DNS_PACKET_UNICAST_SIZE_MAX 512
+#define DNS_PACKET_UNICAST_SIZE_MAX 512u
 
 /* With EDNS0 we can use larger packets, default to 4096, which is what is commonly used */
-#define DNS_PACKET_UNICAST_SIZE_LARGE_MAX 4096
+#define DNS_PACKET_UNICAST_SIZE_LARGE_MAX 4096u
 
 struct DnsPacket {
         int n_ref;