pppoe: drop PACKET_OTHERHOST before skb_share_check()

Align with ip_rcv() by dropping PACKET_OTHERHOST packets before
calling skb_share_check(). This avoids unnecessary skb processing
for packets that will be discarded anyway.

Signed-off-by: Qingfang Deng <dqfext@gmail.com>
Acked-by: Guillaume Nault <gnault@redhat.com>
Link: https://patch.msgid.link/20250623033431.408810-1-dqfext@gmail.com


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