fix(dialer): correct inverted setMark on FreeBSD/OpenBSD

Fix setMark early-return conditions that were inverted relative to
Linux: on FreeBSD (SO_USER_COOKIE) and OpenBSD (SO_RTABLE), a
non-zero mark was short-circuited instead of applied, disabling
socket marking entirely.

Also fix GetClientIP to trim leading whitespace from X-Forwarded-For
entries (per RFC 7239), and fix Body.Read to subtract len(b) instead
of n from recordSize when a single read exceeds the remaining quota.

Add unit tests for internal/net/ (addr, dialer, http, ip, net, pipe,
transport, resolve, proxyproto, udp).

internal/net/ip/ip_test.go

@@ -0,0 +1,36 @@
+package ip
+
+import (
+	"testing"
+
+	"github.com/songgao/water/waterutil"
+)
+
+func TestProtocol(t *testing.T) {
+	tests := []struct {
+		name string
+		p    waterutil.IPProtocol
+		want string
+	}{
+		{"HOPOPT", waterutil.HOPOPT, "HOPOPT"},
+		{"ICMP", waterutil.ICMP, "ICMP"},
+		{"IGMP", waterutil.IGMP, "IGMP"},
+		{"GGP", waterutil.GGP, "GGP"},
+		{"TCP", waterutil.TCP, "TCP"},
+		{"UDP", waterutil.UDP, "UDP"},
+		{"IPv6-Route", waterutil.IPv6_Route, "IPv6-Route"},
+		{"IPv6-Frag", waterutil.IPv6_Frag, "IPv6-Frag"},
+		{"IPv6-ICMP", waterutil.IPv6_ICMP, "IPv6-ICMP"},
+		{"unknown protocol", waterutil.IPProtocol(255), "unknown(255)"},
+		{"unknown value", waterutil.IPProtocol(100), "unknown(100)"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := Protocol(tt.p)
+			if got != tt.want {
+				t.Errorf("Protocol() = %q, want %q", got, tt.want)
+			}
+		})
+	}
+}