net:core: use IS_ENABLED

Use IS_ENABLED(CONFIG_FOO)
instead of defined(CONFIG_FOO) || defined (CONFIG_FOO_MODULE)

Signed-off-by: Igor Maravić <igorm@etf.rs>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/core/secure_seq.c
Simple merge

diff --cc net/core/skbuff.c
Simple merge