Fix off-by-one overflow in the IP protocol table

[nnposter]

The PR contains the following:

• Fixes protocol_table being defined one element short, which can result in out-of-bounds write. See

  nmap/protocols.cc

  Line 82 in 667527c

  static struct nprotoent *protocol_table[UCHAR_MAX];

  and

  nmap/protocols.cc

  Line 122 in 667527c

  if (res !=2 || protno > UCHAR_MAX) {

• Fixes assertion that prevents out-of-bounds read from the same table, but is actually one off. This has been documented in Assertion failure with IP protocol scan #2896. See

  nmap/protocols.cc

  Line 194 in 667527c

  assert(num >= 0 && num < UCHAR_MAX);

• Implements a new constant, representing the largest allowed IP protocol number, to replace hard-coded integers and other abstractions throughout the Nmap code base. A constant with the same meaning is already defined in libdnet-stripped, but buried relatively deep in includes, so the decision was made to create a new one directly in protocols.h.

The PR does not cover IP protocol handling in Nping.

The PR will be committed after August 25, 2024, unless concerns are raised.

[dmiller-nmap]

Looks good to me. Thanks!

[fyodor]

Thanks @nnposter! Please do merge.

[nnposter]

Committed as r38951.