make "linux kernel" connections configurable

Sometimes when a new connection is about to be established, we don't get
the PID of the process using the eBPF proc monitor method. But in some
rare situations, the kernel still holds information about the connection
(sock_diag struct basically). We assume that these connections are
initiated from kernel space.

Per some debugging, this doesn't seem to be always the root cause, so
these connections will only be shown if InterceptUnknown config field is
set to true.

daemon/procmon/parse.go

@@ -85,7 +85,7 @@ func GetPIDFromINode(inode int, inodeKey string) int {
 // If it exists in /proc, a new Process{} object is returned with  the details
 // to identify a process (cmdline, name, environment variables, etc).
 func FindProcess(pid int, interceptUnknown bool) *Process {
-	if pid == -100 {
+	if interceptUnknown && pid == -100 {
 		return NewProcess(-100, "Linux kernel")
 	}
 	if interceptUnknown && pid < 0 {