Changes

contrib/systemd: AmbientCapabilities=CAP_NET_ADMIN

Set CAP_NET_ADMIN so osmo-upf can set up GTP tunends and tunmaps even if
running as user.

Fix for:
  Operation not permitted (you must be root)
  netlink: Error: cache initialization failed: Operation not permitted
  20240430095022378 DNFT ERROR error running nft ruleset: rc=-1 ruleset="add table inet osmo-upf { flags owner; };\n" (upf_nft.c:79)
  20240430095022378 DNFT ERROR Failed to create nft table "osmo-upf" (upf_nft.c:111)

Fixes: OS#6444
Change-Id: I17b21ad92837ad360d667248f3f002d44251891c