ebpf: Updated eBPF program and skeleton.

Updated section name, so libbpf should init/gues proper
program type without specifications during open/load.
Also, added map_flags with explicitly declared BPF_F_MMAPABLE.
Added check for BPF_F_MMAPABLE flag to meson script and
requirements to libbpf version.
Also changed fragmentation flag check - some TCP/UDP packets
may be considered fragmented if DF flag is set.

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>