net: ip_gre: Fix spelling mistake "demultiplexor" -> "demultiplexer"

There is a spelling mistake in a pr_info message. Fix it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://patch.msgid.link/20250423113719.173539-1-colin.i.king@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>