Add bpf_syscall_wrappers for tethering apex and update allowed-deps.txt

Split the BPF system calls header definition into a new header library
(bpf_syscall_wrappers). Both platform and tethering apex require the
BPF system call definition. Move the definition from system/bpf/
libbpf_android/include/bpf/BpfUtils.h to frameworks/libs/net/
common/native/bpf_syscall_wrappers

Test: build, flash and run atest BpfMapTest
Change-Id: Ief5ffbb96c216796e4f0f4cacbde7c08f4af274a