bsnmp: make single bit bitfields unsigned to avoid clang 16 warning

Clang 16 introduced a warning about single bit bitfields in structs,
which is triggered by a declaration in bsnmp's snmpd.h:

contrib/bsnmp/snmpd/trans_lsock.c:271:21: error: implicit truncation from 'int' to a one-bit wide bit-field changes value from 1 to -1 [-Werror,-Wsingle-bit-bitfield-constant-conversion]
        peer->input.stream = 1;
                           ^ ~

Signed one-bit bitfields can only have values -1 and 0, but the intent
here is to use the field as a boolean, so make it unsigned.

MFC after: 3 days

(cherry picked from commit b740e02500ca248e1096cf745a17d2a8fcc44fed)