net: always declare __sock_wfree() and tcp_wfree()

net: always declare __sock_wfree() and tcp_wfree()

Even if guarded by IS_ENABLED(CONFIG_INET) compilers need to know
what __sock_wfree() and tcp_wfree() are:

   include/net/sock.h:1861:63: note: each undeclared identifier is reported only once for each function it appears in
   include/net/sock.h:1862:63: error: 'tcp_wfree' undeclared (first use in this function); did you mean 'sock_wfree'?
    1862 |                (IS_ENABLED(CONFIG_INET) && skb->destructor == tcp_wfree);

Fixes: f0de88303d5e ("net: make is_skb_wmem() available to modules")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202605141607.mDXnYFKY-lkp@intel.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260514095506.3919094-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>