Using the 64-bit Linux capability mode when available.
Using the 64-bit Linux capability mode when available.

For backward compatibility, the Linux capabilities macros exposes v1 semantics
(32-bit) by default.  We probe the version at runtime (because of pre-compiled
binaries) but the kernel syscall API is conservative and it doesn't return a
64-bit capability version if the input version is v1.

This patch suppress the kernel > 5.0 dmesg log below:

  capability: warning: 'unitd' uses 32-bit capabilities (legacy support in use)

nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit