all: adjust case of "IPv4" and "IPv6"

Updates #docs

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

api.md

@@ -101,8 +101,8 @@ You can also [list all devices in the tailnet](#list-tailnet-devices) to get the
 ``` jsonc
 {
   // addresses (array of strings) is a list of Tailscale IP
-  // addresses for the device, including both ipv4 (formatted as 100.x.y.z)
-  // and ipv6 (formatted as fd7a:115c:a1e0:a:b:c:d:e) addresses.
+  // addresses for the device, including both IPv4 (formatted as 100.x.y.z)
+  // and IPv6 (formatted as fd7a:115c:a1e0:a:b:c:d:e) addresses.
   "addresses": [
     "100.87.74.78",
     "fd7a:115c:a1e0:ac82:4843:ca90:697d:c36e"

net/dns/resolver/tsdns.go

@@ -724,7 +724,7 @@ func (r *Resolver) parseViaDomain(domain dnsname.FQDN, typ dns.Type) (netip.Addr
 		return netip.Addr{}, false // badly formed, don't respond
 	}
 
-	// MapVia will never error when given an ipv4 netip.Prefix.
+	// MapVia will never error when given an IPv4 netip.Prefix.
 	out, _ := tsaddr.MapVia(uint32(prefix), netip.PrefixFrom(ip4, ip4.BitLen()))
 	return out.Addr(), true
 }

net/netmon/netmon_linux.go

@@ -100,7 +100,7 @@ func (c *nlConn) Receive() (message, error) {
 				typ = "RTM_DELADDR"
 			}
 
-			// label attributes are seemingly only populated for ipv4 addresses in the wild.
+			// label attributes are seemingly only populated for IPv4 addresses in the wild.
 			label := rmsg.Attributes.Label
 			if label == "" {
 				itf, err := net.InterfaceByIndex(int(rmsg.Index))

wgengine/router/router_linux.go

@@ -1647,7 +1647,7 @@ func checkIPv6(logf logger.Logf) error {
 	}
 	bs, err := os.ReadFile("/proc/sys/net/ipv6/conf/all/disable_ipv6")
 	if err != nil {
-		// Be conservative if we can't find the ipv6 configuration knob.
+		// Be conservative if we can't find the IPv6 configuration knob.
 		return err
 	}
 	disabled, err := strconv.ParseBool(strings.TrimSpace(string(bs)))