pppd crashes when running from the NM 1.10 snap

It has been detected that pppd crashes when running confined inside the NM 1.10 snap. This happens because it cannot open/create a file in called /var/run/pppd2.tdb, which triggers a bug later.

This is the backtrace:

#0 0x00005581bd1031e9 in tdb_close (tdb=0x0) at tdb.c:1872
#1 0x00005581bd0d8e81 in safe_fork (infd=10, outfd=10, errfd=10) at main.c:1571
#2 0x00005581bd0d9393 in run_program (prog=prog@entry=0x5581bd3692a0 <path_ipup> "/etc/ppp/ip-up", args=args@entry=0x7ffca0b31bf0, must_exist=must_exist@entry=0, done=done@entry=0x5581bd0e1d10 <ipcp_script_done>, arg=arg@entry=0x0, wait=wait@entry=0) at main.c:1798
#3 0x00005581bd0dfa4b in ipcp_script (script=0x5581bd3692a0 <path_ipup> "/etc/ppp/ip-up", wait=0) at ipcp.c:2140
#4 0x00005581bd0daa38 in fsm_rtermack (f=<optimized out>) at fsm.c:658
#5 0x00005581bd0daa38 in fsm_input (f=0x5581bd368dc0 <ipcp_fsm>, inpacket=0x5581bd327464 <inpacket_buf+4> "\002\024", l=<optimized out>) at fsm.c:393
#6 0x00005581bd0d7563 in get_input () at main.c:1085
#7 0x00005581bd0d7563 in main (argc=<optimized out>, argv=<optimized out>) at main.c:537

Proposed fix upstream: https://github.com/paulusmack/ppp/pull/122