Fix printf format specifiers which cause issues on Windows

[fippo]

see e.g Firefox, Chromium ran into the same problem:
https://phabricator.services.mozilla.com/D289571

[fippo]

error gets caught by -Wformat apparently, from Chromium compile attempts:

[3290/83691] CC obj/third_party/libsrtp/libsrtp/srtp.obj
..\..\third_party\llvm-build\Release+Asserts\bin\clang-cl.exe /c ../../third_party/libsrtp/srtp/srtp.c /nologo /showIncludes:user /winsysroot....(too long)
../../third_party/libsrtp/srtp/srtp.c(667,60): error: format specifies type 'unsigned int' but the argument has type 'u_long' (aka 'unsigned long') [-Werror,-Wformat]
  667 |     debug_print(mod_srtp, "cloning stream (SSRC: 0x%08x)", ntohl(ssrc));

[fippo]

(fixed like it is fixed in 3.x, not how Mozilla did it)