bpf: Update BPF LSM maintainer list

After catching up with KP recently, we discussed that I will be now be
responsible for co-maintaining the BPF LSM. Adding myself as
designated maintainer of the BPF LSM, and specifying more files in
which the BPF LSM maintenance responsibilities should now extend out
to. This is at the back of all the BPF kfuncs that have been added
recently, which are fundamentally restricted to being used only from
BPF LSM program types.

Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/ZnA-1qdtXS1TayD7@google.com