pcap: Check return codes of buffer_add_* functions.
pcap: Check return codes of buffer_add_* functions.

Found by Coverity.

pouete/libssh,wangshawn/libssh,mwgoldsmith/ssh,pouete/libssh,robxu9/libssh,elastichosts/libssh,pouete/libssh,taikoo/libssh,robxu9/libssh,mwgoldsmith/ssh,sebadoom/libssh,nviennot/libssh,Distrotech/libssh,taikoo/libssh,mwgoldsmith/libssh,taikoo/libssh,jt1/honeypot-libssh,Distrotech/libssh,pouete/libssh,jt1/honeypot-libssh,jt1/honeypot-libssh,mwgoldsmith/libssh,bigcat26/libssh-mod,sebadoom/libssh,kedazo/libssh,mwgoldsmith/ssh,sebadoom/libssh,taikoo/libssh,mwgoldsmith/ssh,kedazo/libssh,wangshawn/libssh,DouglasHeriot/libssh,elastichosts/libssh,nviennot/libssh,robxu9/libssh,jt1/honeypot-libssh,mwgoldsmith/libssh,DouglasHeriot/libssh,DouglasHeriot/libssh,wangshawn/libssh,DouglasHeriot/libssh,bigcat26/libssh-mod,Distrotech/libssh,nviennot/libssh,kedazo/libssh,mwgoldsmith/libssh,wangshawn/libssh,Distrotech/libssh,kedazo/libssh,sebadoom/libssh,robxu9/libssh,elastichosts/libssh,nviennot/libssh,bigcat26/libssh-mod,bigcat26/libssh-mod