network: fix static assertion on IPPROTO_MAX range

Builds with recent glibc would fail with:
../src/network/netdev/fou-tunnel.c: In function ‘config_parse_ip_protocol’:
../src/basic/macro.h:380:9: error: static assertion failed: "IPPROTO_MAX-1 <= UINT8_MAX"
  380 |         static_assert(expr, #expr)
      |         ^~~~~~~~~~~~~
../src/network/netdev/fou-tunnel.c:161:9: note: in expansion of macro ‘assert_cc’
  161 |         assert_cc(IPPROTO_MAX-1 <= UINT8_MAX);
      |         ^~~~~~~~~

This is because f9ac84f92f151e07586c55e14ed628d493a5929d (present in
glibc-2.31.9000-9.fc33.x86_64) added IPPROTO_MPTCP=262, following
v5.5-rc5-1002-gfaf391c382 in the kernel.

(cherry picked from commit 3d58d732)
(cherry picked from commit c5e34690)
(cherry picked from commit cc8aeb99)