x86/apic: Inline __x2apic_send_IPI_dest()

x86/apic: Inline __x2apic_send_IPI_dest()

Avoid one call/ret in networking RPS/RFS fast path, with no space cost.

scripts/bloat-o-meter -t vmlinux.before vmlinux.after
add/remove: 0/2 grow/shrink: 2/0 up/down: 96/-97 (-1)
Function                                     old     new   delta
x2apic_send_IPI                              146     198     +52
__x2apic_send_IPI_mask                       326     370     +44
__pfx___x2apic_send_IPI_dest                  16       -     -16
__x2apic_send_IPI_dest                        81       -     -81
Total: Before=20861234, After=20861233, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20251223052026.4141498-1-edumazet@google.com