sshbuf_poke_u16
ASSERT_INT_EQ(sshbuf_poke_u16(p1, 0, 0xa1b2), 0);
ASSERT_INT_EQ(sshbuf_poke_u16(p1, 8, 0xa1b2), 0);
ASSERT_INT_EQ(sshbuf_poke_u16(p1, 9, 0xa1b2),
ASSERT_INT_EQ(sshbuf_poke_u16(p1, 10, 0xa1b2),
ASSERT_INT_EQ(sshbuf_poke_u16(p1, 1000, 0xa1b2),
int sshbuf_poke_u16(struct sshbuf *buf, size_t offset, uint16_t val);