core: rename socket-bind.[ch] → bpf-socket-bind.[ch]

The other BPF infra has a file name prefix of "bpf-" hence do so here
too.

src/core/bpf-socket-bind.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+#pragma once
+
+#include "fdset.h"
+#include "unit.h"
+
+int bpf_socket_bind_supported(void);
+
+/* Add BPF link fd created before daemon-reload or daemon-reexec.  FDs will be closed at the end of
+ * socket_bind_install. */
+int bpf_socket_bind_add_initial_link_fd(Unit *u, int fd);
+
+int bpf_socket_bind_install(Unit *u);
+
+int bpf_serialize_socket_bind(Unit *u, FILE *f, FDSet *fds);