net/tap: set BPF syscall ID for LoongArch

Define the missing __NR_bpf syscall id to enable the tap PMD on
LoongArch.

Signed-off-by: Min Zhou <zhoumin@loongson.cn>

drivers/net/tap/meson.build

@@ -1,12 +1,6 @@
 # SPDX-License-Identifier: BSD-3-Clause
 # Copyright 2018 Luca Boccassi <bluca@debian.org>
 
-if arch_subdir == 'loongarch'
-    build = false
-    reason = 'not supported on LoongArch'
-    subdir_done()
-endif
-
 if not is_linux
     build = false
     reason = 'only supported on Linux'

drivers/net/tap/tap_bpf.h

@@ -103,6 +103,8 @@ union bpf_attr {
 #  define __NR_bpf 361
 # elif defined(__riscv)
 #  define __NR_bpf 280
+# elif defined(__loongarch__)
+#  define __NR_bpf 280
 # else
 #  error __NR_bpf not defined
 # endif