libbpf: Fix libbpf_common.h when installing libbpf through 'make install'

This fixes two issues with the newly introduced libbpf_common.h file:

- The header failed to include <string.h> for the definition of memset()
- The new file was not included in the install_headers rule in the Makefile

Both of these issues cause breakage when installing libbpf with 'make
install' and trying to use it in applications.

Fixes: 544402d4b493 ("libbpf: Extract common user-facing helpers")
Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Yonghong Song <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

0 files changed, 0 insertions, 0 deletions