bpf: Fix net/core/filter build errors when INET is not enabled

Fix build errors when CONFIG_INET is not set/enabled.

(.text+0x2b1b): undefined reference to `tcp_prot'
(.text+0x2b3b): undefined reference to `tcp_prot'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/b1a858ec-7e04-56bc-248a-62cb9bbee726@infradead.org