net: inline napi_skb_cache_get()

net: inline napi_skb_cache_get()

clang is inlining it already, gcc (14.2) does not.

Small space cost (215 bytes on x86_64) but faster sk_buff allocations.

$ scripts/bloat-o-meter -t net/core/skbuff.gcc.before.o net/core/skbuff.gcc.after.o
add/remove: 0/1 grow/shrink: 4/1 up/down: 359/-144 (215)
Function                                     old     new   delta
__alloc_skb                                  471     611    +140
napi_build_skb                               245     363    +118
napi_alloc_skb                               331     416     +85
skb_copy_ubufs                              1869    1885     +16
skb_shift                                   1445    1413     -32
napi_skb_cache_get                           112       -    -112
Total: Before=59941, After=60156, chg +0.36%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260112131515.4051589-1-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>