[socket] use "this" pointer in memset while initialization SockAddr (#3413)
[socket] use "this" pointer in memset while initialization SockAddr (#3413)

This change helps address a coverity warning (about memory overrun).
srickardti/openthread,lanyuwen/openthread,lanyuwen/openthread,librasungirl/openthread,erja-gp/openthread,abtink/openthread,bukepo/openthread,abtink/openthread,erja-gp/openthread,erja-gp/openthread,bukepo/openthread,openthread/openthread,jwhui/openthread,erja-gp/openthread,turon/openthread,lanyuwen/openthread,turon/openthread,librasungirl/openthread,abtink/openthread,chshu/openthread,chshu/openthread,openthread/openthread,turon/openthread,srickardti/openthread,erja-gp/openthread,turon/openthread,abtink/openthread,openthread/openthread,srickardti/openthread,openthread/openthread,bukepo/openthread,erja-gp/openthread,lanyuwen/openthread,chshu/openthread,jwhui/openthread,jwhui/openthread,chshu/openthread,bukepo/openthread,librasungirl/openthread,librasungirl/openthread,chshu/openthread,lanyuwen/openthread,jwhui/openthread,srickardti/openthread,lanyuwen/openthread,chshu/openthread