kernel-selftest: add dependency on libcap

* vm selftest uses it as well:
i586-webos-linux-gcc -m32 -march=i586 -fstack-protector-strong -Wformat -Wformat-security -Werror=format-security --sysroot=kernel-selftest/1.0-r0/recipe-sysroot -Wall -I ../../../../usr/include -Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed -fstack-protector-strong -Wl,-z,relro,-z,now mlock-random-test.c -lrt -lcap -o kernel-selftest/1.0-r0/kernel-selftest-1.0/tools/testing/selftests/vm/mlock-random-test
mlock-random-test.c:8:10: fatal error: sys/capability.h: No such file or directory

 #include <sys/capability.h>
          ^~~~~~~~~~~~~~~~~~

compilation terminated.

---
 meta-oe/recipes-kernel/kernel-selftest/kernel-selftest.bb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 34a869d1fe..e92f3d8ca4 100644
@@ -18,7 +18,7 @@ SRC_URI_libc-musl += "file://userfaultfd.patch \
 PACKAGECONFIG ??= "bpf vm"
 
 PACKAGECONFIG[bpf] = ",,elfutils libcap libcap-ng rsync-native,"
-PACKAGECONFIG[vm] = ",,,libgcc bash"
+PACKAGECONFIG[vm] = ",,libcap,libgcc bash"
 
 do_patch[depends] += "virtual/kernel:do_shared_workdir"
 

2.17.1