Setcap: failed to set capabilites

When I try to use setcap on a file, I get an errormessage:

setcap cap_fowner,cap_mknod,cap_sys_chroot=ep /filename
Failed to set capabilities on file `/filename' (Not supported)
usage: setcap [-q] [-v] [-n <rootid>] (-r|-|<caps>) <filename> [ ... (-r|-|<capsN>) <filenameN> ]

 Note <filename> must be a regular (non-symlink) file.

I have checked that /filename is a regular file and extended attributes are enabled on my filesystem. Any idea what went wrong?

I am using openwrt 18.06.4. I have compiled libcap with the executables.

No "complete answer" there that I saw, but

Is there perhaps a kernel tunable that needs to be set as well?

@alex1452 This is not an answer to your question, I'm sorry. But I have a question for you, if you don't mind.

You said you compiled libcap with the executables. I did the same, checking (Y) in both libcap and the executables in make menuconfig (SDK).
However, the make only resulted in libcap_2.25-2_x86_64.ipk and when I installed it in my router, no setcap command was found.
What file(s) did you transfer to the OpenWrt machine so you could have setcap capabilities? Was it just the libpcap .ipk or another one too?