ipv4: fib: Remove unnecessary encap_type check

lwtunnel_build_state() has check validity of encap_type,
so no need to do this before call it.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20250625022059.3958215-1-yuehaibing@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>