MAINTAINERS: Adjust entry in XDP SOCKETS to actual file name

MAINTAINERS: Adjust entry in XDP SOCKETS to actual file name

Commit 2b43470add8c ("xsk: Introduce AF_XDP buffer allocation API") added a
new header file include/net/xsk_buff_pool.h, but commit 28bee21dc04b
("MAINTAINERS, xsk: Update AF_XDP section after moves/adds") added a file
entry referring to include/net/xsk_buffer_pool.h.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains:

  warning: no file matches  F:  include/net/xsk_buffer_pool.h

Adjust the entry in XDP SOCKETS to the actual file name.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200525141553.7035-1-lukas.bulwahn@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>