bpf: Do not reopen map fd if already open
bpf: Do not reopen map fd if already open

Also get rid of isOpen member and use m.fd! = 0 to check if map has been
opened already.

Signed-off-by: Thomas Graf <5f50a84c1fa3bcff146405017f36aec1a10a9e38@cilium.io>

tgraf/cilium,michi-covalent/cilium,mskarbek/cilium,scanf/cilium,gumpt/cilium,ivar-lazzaro/cilium,scanf/cilium,tgraf/cilium,mskarbek/cilium,gumpt/cilium,ivar-lazzaro/cilium,eloycoto/cilium,cilium/cilium,tklauser/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,ivar-lazzaro/cilium,mskarbek/cilium,gumpt/cilium,tgraf/cilium,michi-covalent/cilium,gumpt/cilium,mskarbek/cilium,scanf/cilium,cilium-team/cilium,scanf/cilium,eloycoto/cilium,eloycoto/cilium,ivar-lazzaro/cilium,eloycoto/cilium,tklauser/cilium,ivar-lazzaro/cilium,tgraf/cilium,tklauser/cilium,scanf/cilium,gumpt/cilium,tgraf/cilium,eloycoto/cilium,tklauser/cilium,eloycoto/cilium,mskarbek/cilium,scanf/cilium,gumpt/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,michi-covalent/cilium,cilium/cilium,scanf/cilium,gumpt/cilium,ivar-lazzaro/cilium,eloycoto/cilium,cilium-team/cilium,mskarbek/cilium