net: remove one stac/clac pair from move_addr_to_user()

Convert the get_user() and __put_user() code to the
fast masked_user_access_begin()/unsafe_{get|put}_user()
variant.

This patch increases the performance of an UDP recvfrom()
receiver (netserver) on 120 bytes messages by 7 %
on an AMD EPYC 7B12 64-Core Processor platform.

Presence of audit_sockaddr() makes difficult
to avoid the stac/clac pair in the copy_to_user() call,
this is left for a future patch.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250925230929.3727873-1-edumazet@google.com


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