cleanup global variables and convert none global to static

bpf/types.h

pkg/ebpf/bpf_arm64_bpfel.go

pkg/ebpf/bpf_arm64_bpfel.o

pkg/ebpf/bpf_powerpc_bpfel.go

pkg/ebpf/bpf_powerpc_bpfel.o

pkg/ebpf/bpf_s390_bpfeb.go

pkg/ebpf/bpf_s390_bpfeb.o

pkg/ebpf/bpf_x86_bpfel.go

pkg/ebpf/bpf_x86_bpfel.o